Add touch scrolling modes experimental flags (DEPRECATED)

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 ee1c7c242ef3faae6f696a758241c2a3557443f8..fd6aa31c046eada4e00ada9a81d5a26c4bc33477 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -240,7 +240,9 @@ TouchEventQueue::TouchEventQueue(TouchEventQueueClient* 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_(GetTouchScrollingMode()),
+      absorbing_touch_moves_(false) {
   DCHECK(client);
 }
 
@@ -326,6 +328,7 @@ 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
@@ -345,6 +348,9 @@ 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
@@ -368,6 +374,19 @@ 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)

[jdduke (slow), 2014/01/31 20:01:16]

Could this be racy? If the GSU ack is delayed?  Or is the only consequence that
there might be some lag time when transitioning between absorption states?

[Rick Byers, 2014/02/01 23:09:34]

Yes, this could be racy.  I was thinking it was OK, but upon further reflection
I'm a little worried about the impact of unavoidably triggering overscroll. 
I've add some thoughts on this to the design doc here:
https://docs.google.com/a/chromium.org/document/d/1MGuCb0Lb7UfaDmH44bp9YKVG-C...
and will leave a TODO in the code for now.  I think this is fine for
experimentation purposes (worst case should cause some minor UI glitches when
under load), but we should resolve it before deciding whether to ship this or
not.

+    return;
+
+  if (event.event.type != blink::WebInputEvent::GestureScrollUpdate)
+    return;
+
+  // Suspend sending touchmove events as long as the scroll events are handled.
+  absorbing_touch_moves_ = (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED);
+}
+
 void TouchEventQueue::OnHasTouchEventHandlers(bool has_handlers) {
   DCHECK(!dispatching_touch_ack_);
   DCHECK(!dispatching_touch_);
@@ -478,6 +497,9 @@ bool TouchEventQueue::ShouldForwardToRenderer(
     return false;
   }
 
+  if (absorbing_touch_moves_ && event.type == WebInputEvent::TouchMove)
+    return false;
+
   // Touch press events should always be forwarded to the renderer.
   if (event.type == WebInputEvent::TouchStart)
     return true;
@@ -523,4 +545,20 @@ void TouchEventQueue::UpdateTouchAckStates(const WebTouchEvent& event,
   }
 }
 
+// static
+TouchEventQueue::TouchScrollingMode TouchEventQueue::GetTouchScrollingMode()

[jdduke (slow), 2014/01/31 20:01:16]

Any reason not to just put this in the anon namespace above and remove the
static member?  Or even better, have the mode be an arg to the TEQ and move
commandline parsing to the InputRouter?

[Rick Byers, 2014/02/01 23:09:34]

Done.

+{
+  std::string modeString = CommandLine::ForCurrentProcess()->
+      GetSwitchValueASCII(switches::kTouchScrollingMode);
+  if (modeString == switches::kTouchScrollingModeSyncTouchmove)
+    return TOUCH_SCROLLING_MODE_SYNC_TOUCHMOVE;
+  if (modeString == switches::kTouchScrollingModeAbsorbTouchmove)
+    return TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE;
+  if (modeString != "" &&
+      modeString != switches::kTouchScrollingModeTouchcancel)
+    LOG(ERROR) << "Invalid --touch-scrolling-mode option: " << modeString;
+  return TOUCH_SCROLLING_MODE_TOUCHCANCEL;
+}
+
+
 }  // namespace content