Add touch scrolling modes experimental flags

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 b32537dd228fac517ef3b59f82d8e20670e9bd07..9924c903a26318e2d91e177f8ded5cf83e9b1a60 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -288,6 +288,7 @@ class CoalescedWebTouchEvent {
 };
 
 TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
+                                 TouchScrollingMode mode,
                                  double touchmove_suppression_length_dips)
     : client_(client),
       dispatching_touch_ack_(NULL),
@@ -295,7 +296,9 @@ TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
       touch_filtering_state_(TOUCH_FILTERING_STATE_DEFAULT),
       ack_timeout_enabled_(false),
       touchmove_slop_suppressor_(
-          new TouchMoveSlopSuppressor(touchmove_suppression_length_dips)) {
+          new TouchMoveSlopSuppressor(touchmove_suppression_length_dips)),
+      absorbing_touch_moves_(false),
+      touch_scrolling_mode_(mode) {
   DCHECK(client);
 }
 
@@ -398,6 +401,7 @@ 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
@@ -417,6 +421,9 @@ 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
@@ -440,6 +447,25 @@ 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).  Worst case, the
+  // delay in updating the absorption state should only 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_);
@@ -549,6 +575,9 @@ 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;