Consuming a touch move prevents only the next scroll update.

content/browser/renderer_host/input/touch_event_queue.cc

Index: content/browser/renderer_host/input/touch_event_queue.cc
diff --git a/content/browser/renderer_host/input/touch_event_queue.cc b/content/browser/renderer_host/input/touch_event_queue.cc
index 61166815b2b171010adafe566bca6d9063ee7bff..41fbaacf33db69b59be82cbcc6fbedc0de349592 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -292,12 +292,15 @@ class CoalescedWebTouchEvent {
   DISALLOW_COPY_AND_ASSIGN(CoalescedWebTouchEvent);
 };
 
-TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client)
+TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
+                                 TouchScrollingMode mode)
     : client_(client),
       dispatching_touch_ack_(NULL),
       dispatching_touch_(false),
       touch_filtering_state_(TOUCH_FILTERING_STATE_DEFAULT),
-      ack_timeout_enabled_(false) {
+      ack_timeout_enabled_(false),
+      touch_scrolling_mode_(mode),
+      absorbing_touch_moves_(false) {
   DCHECK(client);
 }
 
@@ -401,6 +404,7 @@ void TouchEventQueue::ForwardToRenderer(
         ack_timeout_enabled_ ? FORWARD_TOUCHES_UNTIL_TIMEOUT
                              : FORWARD_ALL_TOUCHES;
     touch_ack_states_.clear();
+    absorbing_touch_moves_ = false;
   }
 
   // A synchronous ack will reset |dispatching_touch_|, in which case
@@ -420,6 +424,9 @@ void TouchEventQueue::OnGestureScrollEvent(
   if (gesture_event.event.type != blink::WebInputEvent::GestureScrollBegin)
     return;
 
+  if (touch_scrolling_mode_ != TOUCH_SCROLLING_MODE_TOUCHCANCEL)
+    return;
+
   // We assume that scroll events are generated synchronously from
   // dispatching a touch event ack. This allows us to generate a synthetic
   // cancel event that has the same touch ids as the touch event that
@@ -443,6 +450,25 @@ void TouchEventQueue::OnGestureScrollEvent(
           dispatching_touch_ack_->coalesced_event()), true));
 }
 
+void TouchEventQueue::OnGestureEventAck(
+    const GestureEventWithLatencyInfo& event,
+    InputEventAckState ack_result) {
+  if (touch_scrolling_mode_ != TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE)
+    return;
+
+  if (event.event.type != blink::WebInputEvent::GestureScrollUpdate)
+    return;
+
+  // Suspend sending touchmove events as long as the scroll events are handled.
+  // Note that there's no guarantee that this ACK is for the most recent
+  // gesture event (or even part of the current sequence).  Worse case, the
+  // delay in updating the absorption state should onl result in minor UI
+  // glitches.
+  // TODO(rbyers): Define precise timing requirements and potentially implement
+  // mitigations for races.
+  absorbing_touch_moves_ = (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED);
+}
+
 void TouchEventQueue::OnHasTouchEventHandlers(bool has_handlers) {
   DCHECK(!dispatching_touch_ack_);
   DCHECK(!dispatching_touch_);
@@ -568,6 +594,9 @@ TouchEventQueue::FilterBeforeForwarding(const WebTouchEvent& event) {
     return ACK_WITH_NOT_CONSUMED;
   }
 
+  if (absorbing_touch_moves_ && event.type == WebInputEvent::TouchMove)
+    return ACK_WITH_NOT_CONSUMED;
+
   // Touch press events should always be forwarded to the renderer.
   if (event.type == WebInputEvent::TouchStart)
     return FORWARD_TO_RENDERER;