Make touch events uncancelable during fling when they are on the current active scroll layer

cc/input/input_handler.h

 // Copyright 2011 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 CC_INPUT_INPUT_HANDLER_H_
 #define CC_INPUT_INPUT_HANDLER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 87 matching lines @@
     ScrollThread thread;
     uint32_t main_thread_scrolling_reasons;
   };
 
   enum ScrollInputType {
     TOUCHSCREEN,
     WHEEL,
     NON_BUBBLING_GESTURE
   };
 
+  enum TouchStartHitResult { HANDLER, SAME_LAYER, DIFFERENT_LAYER };

[tdresser, 2016/11/04 17:15:20]

These names aren't clear to me. Same layer as what? They need to make sense in
the context of: |DoTouchEventsBlockScrollAt| (or we could rename that method).

Perhaps:
DoTouchHandlersBlockScrollAt(...)
NO_HANDLER
HANDLER
HANDLER_ON_FLINGING_LAYER

Maybe get a second opinion on this - I'm not too fond of the naming here.

+
   // Binds a client to this handler to receive notifications. Only one client
   // can be bound to an InputHandler. The client must live at least until the
   // handler calls WillShutdown() on the client.
   virtual void BindToClient(InputHandlerClient* client) = 0;
 
   // Selects a layer to be scrolled using the |scroll_state| start position.
   // Returns SCROLL_STARTED if the layer at the coordinates can be scrolled,
   // SCROLL_ON_MAIN_THREAD if the scroll event should instead be delegated to
   // the main thread, or SCROLL_IGNORED if there is nothing to be scrolled at
   // the given coordinates.
@@ skipping 64 matching lines @@
   virtual bool IsCurrentlyScrollingViewport() const = 0;
 
   // Whether the layer under |viewport_point| is the currently scrolling layer.
   virtual bool IsCurrentlyScrollingLayerAt(const gfx::Point& viewport_point,
                                            ScrollInputType type) const = 0;
 
   virtual EventListenerProperties GetEventListenerProperties(
       EventListenerClass event_class) const = 0;
 
   // Whether the page should be given the opportunity to suppress scrolling by
   // consuming touch events that started at |viewport_point|.

[tdresser, 2016/11/04 17:15:20]

Update this comment.

[lanwei, 2016/11/11 18:22:45]

Done.

-  virtual bool DoTouchEventsBlockScrollAt(const gfx::Point& viewport_point) = 0;
+  virtual TouchStartHitResult DoTouchEventsBlockScrollAt(
+      const gfx::Point& viewport_point) = 0;
 
   // Calling CreateLatencyInfoSwapPromiseMonitor() to get a scoped
   // LatencyInfoSwapPromiseMonitor. During the life time of the
   // LatencyInfoSwapPromiseMonitor, if SetNeedsRedraw() or SetNeedsRedrawRect()
   // is called on LayerTreeHostImpl, the original latency info will be turned
   // into a LatencyInfoSwapPromise.
   virtual std::unique_ptr<SwapPromiseMonitor>
   CreateLatencyInfoSwapPromiseMonitor(ui::LatencyInfo* latency) = 0;
 
   virtual ScrollElasticityHelper* CreateScrollElasticityHelper() = 0;
 
   // Called by the single-threaded UI Compositor to get or set the scroll offset
   // on the impl side. Retruns false if |layer_id| isn't in the active tree.
   virtual bool GetScrollOffsetForLayer(int layer_id,
                                        gfx::ScrollOffset* offset) = 0;
   virtual bool ScrollLayerTo(int layer_id, const gfx::ScrollOffset& offset) = 0;
 
  protected:
   InputHandler() {}
   virtual ~InputHandler() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InputHandler);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_INPUT_HANDLER_H_