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diff --git a/dom/svg/SVGPointList.h b/dom/svg/SVGPointList.h
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+++ b/dom/svg/SVGPointList.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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_SVGPOINTLIST_H__
+#define MOZILLA_SVGPOINTLIST_H__
+
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsIContent.h"
+#include "nsINode.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsSVGElement.h"
+#include "nsTArray.h"
+#include "SVGPoint.h"
+
+#include <string.h>
+
+namespace mozilla {
+class nsISVGPoint;
+
+/**
+ * ATTENTION! WARNING! WATCH OUT!!
+ *
+ * Consumers that modify objects of this type absolutely MUST keep the DOM
+ * wrappers for those lists (if any) in sync!! That's why this class is so
+ * locked down.
+ *
+ * The DOM wrapper class for this class is DOMSVGPointList.
+ */
+class SVGPointList
+{
+  friend class mozilla::nsISVGPoint;
+  friend class SVGAnimatedPointList;
+  friend class DOMSVGPointList;
+  friend class DOMSVGPoint;
+
+public:
+
+  SVGPointList(){}
+  ~SVGPointList(){}
+
+  // Only methods that don't make/permit modification to this list are public.
+  // Only our friend classes can access methods that may change us.
+
+  /// This may return an incomplete string on OOM, but that's acceptable.
+  void GetValueAsString(nsAString& aValue) const;
+
+  bool IsEmpty() const {
+    return mItems.IsEmpty();
+  }
+
+  uint32_t Length() const {
+    return mItems.Length();
+  }
+
+  const SVGPoint& operator[](uint32_t aIndex) const {
+    return mItems[aIndex];
+  }
+
+  bool operator==(const SVGPointList& rhs) const {
+    // memcmp can be faster than |mItems == rhs.mItems|
+    return mItems.Length() == rhs.mItems.Length() &&
+           memcmp(mItems.Elements(), rhs.mItems.Elements(),
+                  mItems.Length() * sizeof(SVGPoint)) == 0;
+  }
+
+  bool SetCapacity(uint32_t aSize) {
+    return mItems.SetCapacity(aSize, fallible);
+  }
+
+  void Compact() {
+    mItems.Compact();
+  }
+
+  // Access to methods that can modify objects of this type is deliberately
+  // limited. This is to reduce the chances of someone modifying objects of
+  // this type without taking the necessary steps to keep DOM wrappers in sync.
+  // If you need wider access to these methods, consider adding a method to
+  // SVGAnimatedPointList and having that class act as an intermediary so it
+  // can take care of keeping DOM wrappers in sync.
+
+protected:
+
+  /**
+   * This may fail on OOM if the internal capacity needs to be increased, in
+   * which case the list will be left unmodified.
+   */
+  nsresult CopyFrom(const SVGPointList& rhs);
+
+  SVGPoint& operator[](uint32_t aIndex) {
+    return mItems[aIndex];
+  }
+
+  /**
+   * This may fail (return false) on OOM if the internal capacity is being
+   * increased, in which case the list will be left unmodified.
+   */
+  bool SetLength(uint32_t aNumberOfItems) {
+    return mItems.SetLength(aNumberOfItems, fallible);
+  }
+
+private:
+
+  // Marking the following private only serves to show which methods are only
+  // used by our friend classes (as opposed to our subclasses) - it doesn't
+  // really provide additional safety.
+
+  nsresult SetValueFromString(const nsAString& aValue);
+
+  void Clear() {
+    mItems.Clear();
+  }
+
+  bool InsertItem(uint32_t aIndex, const SVGPoint &aPoint) {
+    if (aIndex >= mItems.Length()) {
+      aIndex = mItems.Length();
+    }
+    return !!mItems.InsertElementAt(aIndex, aPoint, fallible);
+  }
+
+  void ReplaceItem(uint32_t aIndex, const SVGPoint &aPoint) {
+    MOZ_ASSERT(aIndex < mItems.Length(),
+               "DOM wrapper caller should have raised INDEX_SIZE_ERR");
+    mItems[aIndex] = aPoint;
+  }
+
+  void RemoveItem(uint32_t aIndex) {
+    MOZ_ASSERT(aIndex < mItems.Length(),
+               "DOM wrapper caller should have raised INDEX_SIZE_ERR");
+    mItems.RemoveElementAt(aIndex);
+  }
+
+  bool AppendItem(SVGPoint aPoint) {
+    return !!mItems.AppendElement(aPoint, fallible);
+  }
+
+protected:
+
+  /* See SVGLengthList for the rationale for using FallibleTArray<SVGPoint> instead
+   * of FallibleTArray<SVGPoint, 1>.
+   */
+  FallibleTArray<SVGPoint> mItems;
+};
+
+
+/**
+ * This SVGPointList subclass is for SVGPointListSMILType which needs a
+ * mutable version of SVGPointList. Instances of this class do not have
+ * DOM wrappers that need to be kept in sync, so we can safely expose any
+ * protected base class methods required by the SMIL code.
+ *
+ * This class contains a strong reference to the element that instances of
+ * this class are being used to animate. This is because the SMIL code stores
+ * instances of this class in nsSMILValue objects, some of which are cached.
+ * Holding a strong reference to the element here prevents the element from
+ * disappearing out from under the SMIL code unexpectedly.
+ */
+class SVGPointListAndInfo : public SVGPointList
+{
+public:
+
+  explicit SVGPointListAndInfo(nsSVGElement *aElement = nullptr)
+    : mElement(do_GetWeakReference(static_cast<nsINode*>(aElement)))
+  {}
+
+  void SetInfo(nsSVGElement *aElement) {
+    mElement = do_GetWeakReference(static_cast<nsINode*>(aElement));
+  }
+
+  nsSVGElement* Element() const {
+    nsCOMPtr<nsIContent> e = do_QueryReferent(mElement);
+    return static_cast<nsSVGElement*>(e.get());
+  }
+
+  /**
+   * Returns true if this object is an "identity" value, from the perspective
+   * of SMIL. In other words, returns true until the initial value set up in
+   * SVGPointListSMILType::Init() has been changed with a SetInfo() call.
+   */
+  bool IsIdentity() const {
+    if (!mElement) {
+      MOZ_ASSERT(IsEmpty(), "target element propagation failure");
+      return true;
+    } 
+    return false;
+  }
+
+  nsresult CopyFrom(const SVGPointListAndInfo& rhs) {
+    mElement = rhs.mElement;
+    return SVGPointList::CopyFrom(rhs);
+  }
+
+  /**
+   * Exposed so that SVGPointList baseVals can be copied to
+   * SVGPointListAndInfo objects. Note that callers should also call
+   * SetElement() when using this method!
+   */
+  nsresult CopyFrom(const SVGPointList& rhs) {
+    return SVGPointList::CopyFrom(rhs);
+  }
+  const SVGPoint& operator[](uint32_t aIndex) const {
+    return SVGPointList::operator[](aIndex);
+  }
+  SVGPoint& operator[](uint32_t aIndex) {
+    return SVGPointList::operator[](aIndex);
+  }
+  bool SetLength(uint32_t aNumberOfItems) {
+    return SVGPointList::SetLength(aNumberOfItems);
+  }
+
+private:
+  // We must keep a weak reference to our element because we may belong to a
+  // cached baseVal nsSMILValue. See the comments starting at:
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=515116#c15
+  // See also https://bugzilla.mozilla.org/show_bug.cgi?id=653497
+  nsWeakPtr mElement;
+};
+
+} // namespace mozilla
+
+#endif // MOZILLA_SVGPOINTLIST_H__