Move overscroll bounce to impl thread

content/renderer/input/input_scroll_elasticity_controller.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_RENDERER_INPUT_SCROLL_ELASTICITY_CONTROLLER_IMPL_H_
+#define CONTENT_RENDERER_INPUT_SCROLL_ELASTICITY_CONTROLLER_IMPL_H_
+
+#include "cc/input/scroll_elasticity_controller.h"
+#include "third_party/WebKit/public/web/WebInputEvent.h"
+
+namespace content {
+
+class InputScrollElasticityController
+    : public cc::ScrollElasticityController {
+public:
+    explicit InputScrollElasticityController(cc::ScrollElasticityControllerClient*);
+    virtual ~InputScrollElasticityController();
+
+    // This method is responsible for both scrolling and rubber-banding.
+    //
+    // Events are passed by IPC from the embedder. Events on Mac are grouped
+    // into "gestures". If this method returns 'true', then this object has
+    // handled the event. It expects the embedder to continue to forward events
+    // from the gesture.
+    //
+    // This method makes the assumption that there is only 1 input device being
+    // used at a time. If the user simultaneously uses multiple input devices,
+    // Cocoa does not correctly pass all the gestureBegin/End events. The state
+    // of this class is guaranteed to become eventually consistent, once the
+    // user stops using multiple input devices.
+    bool handleWheelEvent(const blink::WebMouseWheelEvent&);
+
+    // cc::ScrollElasticityController implementation:
+    void WillShutdown() override;
+    void Animate(base::TimeTicks time) override;
+
+private:
+
+    void snapRubberBandTimerFired();
+    bool isRubberBandInProgress() const;
+
+    void stopSnapRubberbandTimer();
+    void snapRubberBand();
+
+    // This method determines whether a given event should be handled. The
+    // logic for control events of gestures (PhaseBegan, PhaseEnded) is handled
+    // elsewhere.
+    //
+    // This class handles almost all wheel events. All of the following
+    // conditions must be met for this class to ignore an event:
+    // + No previous events in this gesture have caused any scrolling or rubber
+    // banding.
+    // + The event contains a horizontal component.
+    // + The client's view is pinned in the horizontal direction of the event.
+    // + The wheel event disallows rubber banding in the horizontal direction
+    // of the event.
+    bool shouldHandleEvent(const blink::WebMouseWheelEvent&);
+
+    cc::ScrollElasticityControllerClient* m_client;
+
+    // There is an active scroll gesture event. This parameter only gets set to
+    // false after the rubber band has been snapped, and before a new gesture
+    // has begun. A careful audit of the code may deprecate the need for this
+    // parameter.
+    bool m_inScrollGesture;
+    // At least one event in the current gesture has been consumed and has
+    // caused the view to scroll or rubber band. All future events in this
+    // gesture will be consumed and overscrolls will cause rubberbanding.
+    bool m_hasScrolled;
+    bool m_momentumScrollInProgress;
+    bool m_ignoreMomentumScrolls;
+
+    base::Time m_lastMomentumScrollTimestamp;
+    gfx::Vector2dF m_overflowScrollDelta;
+    gfx::Vector2dF m_stretchScrollForce;
+    gfx::Vector2dF m_momentumVelocity;
+
+    // Rubber band state.
+    base::Time m_startTime;
+    gfx::Vector2dF m_startStretch;
+    gfx::Vector2dF m_origOrigin;
+    gfx::Vector2dF m_origVelocity;
+
+    bool m_snapRubberbandTimerIsActive;
+};
+
+}
+
+#endif  // CONTENT_RENDERER_INPUT_SCROLL_ELASTICITY_CONTROLLER_IMPL_H_