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diff --git a/dom/heapsnapshot/DeserializedNode.h b/dom/heapsnapshot/DeserializedNode.h
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+/* -*-  Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_devtools_DeserializedNode__
+#define mozilla_devtools_DeserializedNode__
+
+#include "js/UbiNode.h"
+#include "js/UniquePtr.h"
+#include "mozilla/devtools/CoreDump.pb.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Move.h"
+#include "mozilla/Vector.h"
+
+// `Deserialized{Node,Edge}` translate protobuf messages from our core dump
+// format into structures we can rely upon for implementing `JS::ubi::Node`
+// specializations on top of. All of the properties of the protobuf messages are
+// optional for future compatibility, and this is the layer where we validate
+// that the properties that do actually exist in any given message fulfill our
+// semantic requirements.
+//
+// Both `DeserializedNode` and `DeserializedEdge` are always owned by a
+// `HeapSnapshot` instance, and their lifetimes must not extend after that of
+// their owning `HeapSnapshot`.
+
+namespace mozilla {
+namespace devtools {
+
+class HeapSnapshot;
+
+using NodeId = uint64_t;
+using StackFrameId = uint64_t;
+
+// A `DeserializedEdge` represents an edge in the heap graph pointing to the
+// node with id equal to `DeserializedEdge::referent` that we deserialized from
+// a core dump.
+struct DeserializedEdge {
+  NodeId         referent;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char16_t* name;
+
+  explicit DeserializedEdge(NodeId referent, const char16_t* edgeName = nullptr)
+    : referent(referent)
+    , name(edgeName)
+  { }
+  DeserializedEdge(DeserializedEdge&& rhs);
+  DeserializedEdge& operator=(DeserializedEdge&& rhs);
+
+private:
+  DeserializedEdge(const DeserializedEdge&) = delete;
+  DeserializedEdge& operator=(const DeserializedEdge&) = delete;
+};
+
+// A `DeserializedNode` is a node in the heap graph that we deserialized from a
+// core dump.
+struct DeserializedNode {
+  using EdgeVector = Vector<DeserializedEdge>;
+  using UniqueStringPtr = UniquePtr<char16_t[]>;
+
+  NodeId              id;
+  JS::ubi::CoarseType coarseType;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char16_t*     typeName;
+  uint64_t            size;
+  EdgeVector          edges;
+  Maybe<StackFrameId> allocationStack;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char*         jsObjectClassName;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char*         scriptFilename;
+  // A weak pointer to this node's owning `HeapSnapshot`. Safe without
+  // AddRef'ing because this node's lifetime is equal to that of its owner.
+  HeapSnapshot*       owner;
+
+  DeserializedNode(NodeId id,
+                   JS::ubi::CoarseType coarseType,
+                   const char16_t* typeName,
+                   uint64_t size,
+                   EdgeVector&& edges,
+                   Maybe<StackFrameId> allocationStack,
+                   const char* className,
+                   const char* filename,
+                   HeapSnapshot& owner)
+    : id(id)
+    , coarseType(coarseType)
+    , typeName(typeName)
+    , size(size)
+    , edges(Move(edges))
+    , allocationStack(allocationStack)
+    , jsObjectClassName(className)
+    , scriptFilename(filename)
+    , owner(&owner)
+  { }
+  virtual ~DeserializedNode() { }
+
+  DeserializedNode(DeserializedNode&& rhs)
+    : id(rhs.id)
+    , coarseType(rhs.coarseType)
+    , typeName(rhs.typeName)
+    , size(rhs.size)
+    , edges(Move(rhs.edges))
+    , allocationStack(rhs.allocationStack)
+    , jsObjectClassName(rhs.jsObjectClassName)
+    , scriptFilename(rhs.scriptFilename)
+    , owner(rhs.owner)
+  { }
+
+  DeserializedNode& operator=(DeserializedNode&& rhs)
+  {
+    MOZ_ASSERT(&rhs != this);
+    this->~DeserializedNode();
+    new(this) DeserializedNode(Move(rhs));
+    return *this;
+  }
+
+  // Get a borrowed reference to the given edge's referent. This method is
+  // virtual to provide a hook for gmock and gtest.
+  virtual JS::ubi::Node getEdgeReferent(const DeserializedEdge& edge);
+
+  struct HashPolicy;
+
+protected:
+  // This is only for use with `MockDeserializedNode` in testing.
+  DeserializedNode(NodeId id, const char16_t* typeName, uint64_t size)
+    : id(id)
+    , coarseType(JS::ubi::CoarseType::Other)
+    , typeName(typeName)
+    , size(size)
+    , edges()
+    , allocationStack(Nothing())
+    , jsObjectClassName(nullptr)
+    , scriptFilename(nullptr)
+    , owner(nullptr)
+  { }
+
+private:
+  DeserializedNode(const DeserializedNode&) = delete;
+  DeserializedNode& operator=(const DeserializedNode&) = delete;
+};
+
+static inline js::HashNumber
+hashIdDerivedFromPtr(uint64_t id)
+{
+    // NodeIds and StackFrameIds are always 64 bits, but they are derived from
+    // the original referents' addresses, which could have been either 32 or 64
+    // bits long. As such, NodeId and StackFrameId have little entropy in their
+    // bottom three bits, and may or may not have entropy in their upper 32
+    // bits. This hash should manage both cases well.
+    id >>= 3;
+    return js::HashNumber((id >> 32) ^ id);
+}
+
+struct DeserializedNode::HashPolicy
+{
+  using Lookup = NodeId;
+
+  static js::HashNumber hash(const Lookup& lookup) {
+    return hashIdDerivedFromPtr(lookup);
+  }
+
+  static bool match(const DeserializedNode& existing, const Lookup& lookup) {
+    return existing.id == lookup;
+  }
+};
+
+// A `DeserializedStackFrame` is a stack frame referred to by a thing in the
+// heap graph that we deserialized from a core dump.
+struct DeserializedStackFrame {
+  StackFrameId        id;
+  Maybe<StackFrameId> parent;
+  uint32_t            line;
+  uint32_t            column;
+  // Borrowed references to strings owned by this DeserializedStackFrame's
+  // owning HeapSnapshot.
+  const char16_t*     source;
+  const char16_t*     functionDisplayName;
+  bool                isSystem;
+  bool                isSelfHosted;
+  // A weak pointer to this frame's owning `HeapSnapshot`. Safe without
+  // AddRef'ing because this frame's lifetime is equal to that of its owner.
+  HeapSnapshot*       owner;
+
+  explicit DeserializedStackFrame(StackFrameId id,
+                                  const Maybe<StackFrameId>& parent,
+                                  uint32_t line,
+                                  uint32_t column,
+                                  const char16_t* source,
+                                  const char16_t* functionDisplayName,
+                                  bool isSystem,
+                                  bool isSelfHosted,
+                                  HeapSnapshot& owner)
+    : id(id)
+    , parent(parent)
+    , line(line)
+    , column(column)
+    , source(source)
+    , functionDisplayName(functionDisplayName)
+    , isSystem(isSystem)
+    , isSelfHosted(isSelfHosted)
+    , owner(&owner)
+  {
+    MOZ_ASSERT(source);
+  }
+
+  JS::ubi::StackFrame getParentStackFrame() const;
+
+  struct HashPolicy;
+
+protected:
+  // This is exposed only for MockDeserializedStackFrame in the gtests.
+  explicit DeserializedStackFrame()
+    : id(0)
+    , parent(Nothing())
+    , line(0)
+    , column(0)
+    , source(nullptr)
+    , functionDisplayName(nullptr)
+    , isSystem(false)
+    , isSelfHosted(false)
+    , owner(nullptr)
+  { };
+};
+
+struct DeserializedStackFrame::HashPolicy {
+  using Lookup = StackFrameId;
+
+  static js::HashNumber hash(const Lookup& lookup) {
+    return hashIdDerivedFromPtr(lookup);
+  }
+
+  static bool match(const DeserializedStackFrame& existing, const Lookup& lookup) {
+    return existing.id == lookup;
+  }
+};
+
+} // namespace devtools
+} // namespace mozilla
+
+namespace JS {
+namespace ubi {
+
+using mozilla::devtools::DeserializedNode;
+using mozilla::devtools::DeserializedStackFrame;
+
+template<>
+class Concrete<DeserializedNode> : public Base
+{
+protected:
+  explicit Concrete(DeserializedNode* ptr) : Base(ptr) { }
+  DeserializedNode& get() const {
+    return *static_cast<DeserializedNode*>(ptr);
+  }
+
+public:
+  static void construct(void* storage, DeserializedNode* ptr) {
+    new (storage) Concrete(ptr);
+  }
+
+  CoarseType coarseType() const final { return get().coarseType; }
+  Id identifier() const override { return get().id; }
+  bool isLive() const override { return false; }
+  const char16_t* typeName() const override;
+  Node::Size size(mozilla::MallocSizeOf mallocSizeof) const override;
+  const char* jsObjectClassName() const override { return get().jsObjectClassName; }
+  const char* scriptFilename() const final { return get().scriptFilename; }
+
+  bool hasAllocationStack() const override { return get().allocationStack.isSome(); }
+  StackFrame allocationStack() const override;
+
+  // We ignore the `bool wantNames` parameter because we can't control whether
+  // the core dump was serialized with edge names or not.
+  js::UniquePtr<EdgeRange> edges(JSContext* cx, bool) const override;
+
+  static const char16_t concreteTypeName[];
+};
+
+template<>
+class ConcreteStackFrame<DeserializedStackFrame> : public BaseStackFrame
+{
+protected:
+  explicit ConcreteStackFrame(DeserializedStackFrame* ptr)
+    : BaseStackFrame(ptr)
+  { }
+
+  DeserializedStackFrame& get() const {
+    return *static_cast<DeserializedStackFrame*>(ptr);
+  }
+
+public:
+  static void construct(void* storage, DeserializedStackFrame* ptr) {
+    new (storage) ConcreteStackFrame(ptr);
+  }
+
+  uint64_t identifier() const override { return get().id; }
+  uint32_t line() const override { return get().line; }
+  uint32_t column() const override { return get().column; }
+  bool isSystem() const override { return get().isSystem; }
+  bool isSelfHosted(JSContext* cx) const override { return get().isSelfHosted; }
+  void trace(JSTracer* trc) override { }
+  AtomOrTwoByteChars source() const override {
+    return AtomOrTwoByteChars(get().source);
+  }
+  AtomOrTwoByteChars functionDisplayName() const override {
+    return AtomOrTwoByteChars(get().functionDisplayName);
+  }
+
+  StackFrame parent() const override;
+  bool constructSavedFrameStack(JSContext* cx,
+                                MutableHandleObject outSavedFrameStack)
+    const override;
+};
+
+} // namespace ubi
+} // namespace JS
+
+#endif // mozilla_devtools_DeserializedNode__