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

cc/input/input_handler.h

Index: cc/input/input_handler.h
diff --git a/cc/input/input_handler.h b/cc/input/input_handler.h
index d60e9d44c7bcf96a2d4564f9ede5a61b2977b06e..91da4a1a2658ccb106b6528416a6a7a87026b97d 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -104,6 +104,12 @@ class CC_EXPORT InputHandler {
     NON_BUBBLING_GESTURE
   };
 
+  enum class TouchStartEventListenerType {
+    NO_HANDLER,
+    HANDLER,
+    HANDLER_ON_FLINGING_LAYER

[tdresser, 2016/11/24 20:33:38]

Same as previous comment - shouldn't this just be HANDLER_ON_SCROLLING_LAYER?

[lanwei, 2016/11/28 06:20:22]

Done.

+  };
+
   // 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.
@@ -187,9 +193,12 @@ class CC_EXPORT InputHandler {
   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|.
-  virtual bool DoTouchEventsBlockScrollAt(const gfx::Point& viewport_point) = 0;
+  // It returns the type of event listener at the given viewport point. Such as
+  // if the page has a touch handler or not, and whether the page should
+  // suppress scrolling by consuming touch events that started at
+  // |viewport_point|.
+  virtual TouchStartEventListenerType EventListenerTypeForTouchStartAt(
+      const gfx::Point& viewport_point) = 0;
 
   // Calling CreateLatencyInfoSwapPromiseMonitor() to get a scoped
   // LatencyInfoSwapPromiseMonitor. During the life time of the