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diff --git a/dom/events/WheelHandlingHelper.h b/dom/events/WheelHandlingHelper.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_WheelHandlingHelper_h_
+#define mozilla_WheelHandlingHelper_h_
+
+#include "mozilla/Attributes.h"
+#include "mozilla/EventForwards.h"
+#include "nsCoord.h"
+#include "nsIFrame.h"
+#include "nsPoint.h"
+
+class nsIScrollableFrame;
+class nsITimer;
+
+namespace mozilla {
+
+class EventStateManager;
+
+/**
+ * DeltaValues stores two delta values which are along X and Y axis.  This is
+ * useful for arguments and results of some methods.
+ */
+
+struct DeltaValues
+{
+  DeltaValues()
+    : deltaX(0.0)
+    , deltaY(0.0)
+  {
+  }
+
+  DeltaValues(double aDeltaX, double aDeltaY)
+    : deltaX(aDeltaX)
+    , deltaY(aDeltaY)
+  {
+  }
+
+  explicit DeltaValues(WidgetWheelEvent* aEvent);
+
+  double deltaX;
+  double deltaY;
+};
+
+/**
+ * WheelHandlingUtils provides some static methods which are useful at handling
+ * wheel events.
+ */
+
+class WheelHandlingUtils
+{
+public:
+  /**
+   * Returns true if aFrame is a scrollable frame and it can be scrolled to
+   * either aDirectionX or aDirectionY along each axis.  Or if aFrame is a
+   * plugin frame (in this case, aDirectionX and aDirectionY are ignored).
+   * Otherwise, false.
+   */
+  static bool CanScrollOn(nsIFrame* aFrame,
+                          double aDirectionX, double aDirectionY);
+  /**
+   * Returns true if the scrollable frame can be scrolled to either aDirectionX
+   * or aDirectionY along each axis.  Otherwise, false.
+   */
+  static bool CanScrollOn(nsIScrollableFrame* aScrollFrame,
+                          double aDirectionX, double aDirectionY);
+
+private:
+  static bool CanScrollInRange(nscoord aMin, nscoord aValue, nscoord aMax,
+                               double aDirection);
+};
+
+/**
+ * ScrollbarsForWheel manages scrollbars state during wheel operation.
+ * E.g., on some platforms, scrollbars should show only while user attempts to
+ * scroll.  At that time, scrollbars which may be possible to scroll by
+ * operation of wheel at the point should show temporarily.
+ */
+
+class ScrollbarsForWheel
+{
+public:
+  static void PrepareToScrollText(EventStateManager* aESM,
+                                  nsIFrame* aTargetFrame,
+                                  WidgetWheelEvent* aEvent);
+  static void SetActiveScrollTarget(nsIScrollableFrame* aScrollTarget);
+  // Hide all scrollbars (both mActiveOwner's and mActivatedScrollTargets')
+  static void MayInactivate();
+  static void Inactivate();
+  static bool IsActive();
+  static void OwnWheelTransaction(bool aOwn);
+
+protected:
+  static const size_t kNumberOfTargets = 4;
+  static const DeltaValues directions[kNumberOfTargets];
+  static nsWeakFrame sActiveOwner;
+  static nsWeakFrame sActivatedScrollTargets[kNumberOfTargets];
+  static bool sHadWheelStart;
+  static bool sOwnWheelTransaction;
+
+
+  /**
+   * These two methods are called upon eWheelOperationStart/eWheelOperationEnd
+   * events to show/hide the right scrollbars.
+   */
+  static void TemporarilyActivateAllPossibleScrollTargets(
+                EventStateManager* aESM,
+                nsIFrame* aTargetFrame,
+                WidgetWheelEvent* aEvent);
+  static void DeactivateAllTemporarilyActivatedScrollTargets();
+};
+
+/**
+ * WheelTransaction manages a series of wheel events as a transaction.
+ * While in a transaction, every wheel event should scroll the same scrollable
+ * element even if a different scrollable element is under the mouse cursor.
+ *
+ * Additionally, this class also manages wheel scroll speed acceleration.
+ */
+
+class WheelTransaction
+{
+public:
+  static nsIFrame* GetTargetFrame() { return sTargetFrame; }
+  static void EndTransaction();
+  /**
+   * WillHandleDefaultAction() is called before handling aWheelEvent on
+   * aTargetFrame.
+   *
+   * @return    false if the caller cannot continue to handle the default
+   *            action.  Otherwise, true.
+   */ 
+  static bool WillHandleDefaultAction(WidgetWheelEvent* aWheelEvent,
+                                      nsWeakFrame& aTargetWeakFrame);
+  static bool WillHandleDefaultAction(WidgetWheelEvent* aWheelEvent,
+                                      nsIFrame* aTargetFrame)
+  {
+    nsWeakFrame targetWeakFrame(aTargetFrame);
+    return WillHandleDefaultAction(aWheelEvent, targetWeakFrame);
+  }
+  static void OnEvent(WidgetEvent* aEvent);
+  static void Shutdown();
+  static uint32_t GetTimeoutTime();
+
+  static void OwnScrollbars(bool aOwn);
+
+  static DeltaValues AccelerateWheelDelta(WidgetWheelEvent* aEvent,
+                                          bool aAllowScrollSpeedOverride);
+
+protected:
+  static void BeginTransaction(nsIFrame* aTargetFrame,
+                               WidgetWheelEvent* aEvent);
+  // Be careful, UpdateTransaction may fire a DOM event, therefore, the target
+  // frame might be destroyed in the event handler.
+  static bool UpdateTransaction(WidgetWheelEvent* aEvent);
+  static void MayEndTransaction();
+
+  static nsIntPoint GetScreenPoint(WidgetGUIEvent* aEvent);
+  static void OnFailToScrollTarget();
+  static void OnTimeout(nsITimer* aTimer, void* aClosure);
+  static void SetTimeout();
+  static uint32_t GetIgnoreMoveDelayTime();
+  static int32_t GetAccelerationStart();
+  static int32_t GetAccelerationFactor();
+  static DeltaValues OverrideSystemScrollSpeed(WidgetWheelEvent* aEvent);
+  static double ComputeAcceleratedWheelDelta(double aDelta, int32_t aFactor);
+  static bool OutOfTime(uint32_t aBaseTime, uint32_t aThreshold);
+
+  static nsWeakFrame sTargetFrame;
+  static uint32_t sTime; // in milliseconds
+  static uint32_t sMouseMoved; // in milliseconds
+  static nsITimer* sTimer;
+  static int32_t sScrollSeriesCounter;
+  static bool sOwnScrollbars;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_WheelHandlingHelper_h_