Consuming a touch move prevents only the next scroll update.

content/browser/renderer_host/input/touch_event_queue.h

Index: content/browser/renderer_host/input/touch_event_queue.h
diff --git a/content/browser/renderer_host/input/touch_event_queue.h b/content/browser/renderer_host/input/touch_event_queue.h
index 07dee38a48b767474032686cc7240b2a41598ff3..f72a8afe1306886218bec8ec86bfe94e506b2ba0 100644
--- a/content/browser/renderer_host/input/touch_event_queue.h
+++ b/content/browser/renderer_host/input/touch_event_queue.h
@@ -36,9 +36,27 @@ class CONTENT_EXPORT TouchEventQueueClient {
 // A queue for throttling and coalescing touch-events.
 class CONTENT_EXPORT TouchEventQueue {
  public:
+  // Different ways of dealing with touch events during scrolling.
+  // TODO(rbyers): Remove (or otherwise update) this once results of
+  // experiments are complete.  http://crbug.com/328503
+  enum TouchScrollingMode {
+    // Send a touchcancel on scroll start and no further touch events for the
+    // duration of the scroll.  Chrome Android's traditional behavior.
+    TOUCH_SCROLLING_MODE_TOUCHCANCEL,
+    // Send touchmove events throughout a scroll, blocking on each ACK and
+    // using the disposition to determine whether a scroll update should be
+    // sent.  Mobile Safari's default overflow scroll behavior.
+    TOUCH_SCROLLING_MODE_SYNC_TOUCHMOVE,
+    // Like sync, except that consumed scroll events cause subsequent touchmove
+    // events to be suppressed.  Unconsumed scroll events return touchmove
+    // events to being dispatched synchronously (so scrolling may be hijacked
+    // when a scroll limit is reached, and later resumed).
+    TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE

[jdduke (slow), 2014/02/13 16:53:06]

Let's add a TOUCH_SCROLLING_MODE_DEFAULT = TOUCH_SCROLLING_MODE_TOUCHCANCEL that
we use in InputRouterImpl to determine the default mode.

[tdresser, 2014/02/13 18:14:09]

Done.

+  };
 
   // The |client| must outlive the TouchEventQueue.
-  explicit TouchEventQueue(TouchEventQueueClient* client);
+  explicit TouchEventQueue(TouchEventQueueClient* client,
+      TouchScrollingMode mode = TOUCH_SCROLLING_MODE_TOUCHCANCEL);

[jdduke (slow), 2014/02/13 16:53:06]

Nit: No default args, and remove explicit.

[tdresser, 2014/02/13 18:14:09]

Done.

   ~TouchEventQueue();
 
   // Adds an event to the queue. The event may be coalesced with previously
@@ -59,6 +77,10 @@ class CONTENT_EXPORT TouchEventQueue {
   // resume the normal flow of sending touch events to the renderer.
   void OnGestureScrollEvent(const GestureEventWithLatencyInfo& gesture_event);
 
+  void OnGestureEventAck(
+      const GestureEventWithLatencyInfo& event,
+      InputEventAckState ack_result);
+
   // Notifies the queue whether the renderer has at least one touch handler.
   void OnHasTouchEventHandlers(bool has_handlers);
 
@@ -165,6 +187,18 @@ class CONTENT_EXPORT TouchEventQueue {
   // has not yet been preventDefaulted, disabled by default.
   scoped_ptr<TouchMoveSlopSuppressor> touchmove_slop_suppressor_;
 
+  // How touch events are handled during scrolling.  For now this is a global
+  // setting for experimentation, but we may evolve it into an app-controlled
+  // mode.
+  const TouchScrollingMode touch_scrolling_mode_;
+
+  // Whether touchmove events should be dropped due to the
+  // TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE mode.  Note that we can't use
+  // touch_filtering_state_ for this (without adding a few new states and
+  // complicating the code significantly) because it can occur with and without
+  // timeout, and shouldn't cause touchend to be dropped.
+  bool absorbing_touch_moves_;
+
   DISALLOW_COPY_AND_ASSIGN(TouchEventQueue);
 };