Don't treat first touch move differently from future touch moves

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 bbac01c3ebff51081f112419068c5525a4bad5cf..f04ff965604c41ab243d7c47fa018fc451117490 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -349,7 +349,8 @@ TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
       send_touch_events_async_(false),
       needs_async_touchmove_for_outer_slop_region_(false),
       last_sent_touch_timestamp_sec_(0),
-      touch_scrolling_mode_(config.touch_scrolling_mode) {
+  touch_scrolling_mode_(config.touch_scrolling_mode),
+  seen_scroll_update_this_sequence_(false) {
   DCHECK(client);
   if (ack_timeout_enabled_) {
     timeout_handler_.reset(
@@ -534,17 +535,16 @@ void TouchEventQueue::ForwardNextEventToRenderer() {
 
 void TouchEventQueue::OnGestureScrollEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
-  if (gesture_event.event.type != blink::WebInputEvent::GestureScrollBegin)
-    return;
-
-  if (touch_filtering_state_ != DROP_ALL_TOUCHES &&
+  if (gesture_event.event.type == blink::WebInputEvent::GestureScrollBegin &&
+      touch_filtering_state_ != DROP_ALL_TOUCHES &&
       touch_filtering_state_ != DROP_TOUCHES_IN_SEQUENCE) {
     DCHECK(!touchmove_slop_suppressor_->suppressing_touchmoves())
         << "The renderer should be offered a touchmove before scrolling begins";
   }
 
   if (touch_scrolling_mode_ == TOUCH_SCROLLING_MODE_ASYNC_TOUCHMOVE) {
-    if (touch_filtering_state_ != DROP_ALL_TOUCHES &&
+    if (gesture_event.event.type == blink::WebInputEvent::GestureScrollBegin &&
+        touch_filtering_state_ != DROP_ALL_TOUCHES &&
         touch_filtering_state_ != DROP_TOUCHES_IN_SEQUENCE) {
       // If no touch points have a consumer, prevent all subsequent touch events
       // received during the scroll from reaching the renderer. This ensures
@@ -559,14 +559,24 @@ void TouchEventQueue::OnGestureScrollEvent(
       }
     }
 
-    pending_async_touchmove_.reset();
-    send_touch_events_async_ = true;
-    needs_async_touchmove_for_outer_slop_region_ = true;
-    return;
+    if (gesture_event.event.type == blink::WebInputEvent::GestureScrollBegin) {
+      seen_scroll_update_this_sequence_ = false;
+      return;
+    }
+
+    if (gesture_event.event.type == blink::WebInputEvent::GestureScrollUpdate &&
+        !seen_scroll_update_this_sequence_) {
+      pending_async_touchmove_.reset();
+      send_touch_events_async_ = true;
+      needs_async_touchmove_for_outer_slop_region_ = true;
+      return;
+    }
   }
 
-  if (touch_scrolling_mode_ != TOUCH_SCROLLING_MODE_TOUCHCANCEL)
+  if (touch_scrolling_mode_ != TOUCH_SCROLLING_MODE_TOUCHCANCEL ||
+      gesture_event.event.type != blink::WebInputEvent::GestureScrollBegin) {

[jdduke (slow), 2014/07/02 17:46:37]

Hmm, I would think we also want the "first allowed scroll update" logic to apply
to the TOUCH_CANCEL mode, no?  Otherwise, if the page preventDefaults the first
touchmove, we'd still get a GSB which would cancel the touch sequence?

It might be easier if we do the GSB and GSU checks at the very beginning of this
function, and treat the first GSU like we do the first GSB (returning early
otherwise).

[tdresser, 2014/07/04 18:28:17]

Done.

     return;
+  }
 
   // We assume that scroll events are generated synchronously from
   // dispatching a touch event ack. This allows us to generate a synthetic