Use input events to improve vsync scheduling

content/browser/android/content_view_core_impl.cc

Index: content/browser/android/content_view_core_impl.cc
diff --git a/content/browser/android/content_view_core_impl.cc b/content/browser/android/content_view_core_impl.cc
index 0f762944731ee56bbcf1defaac237a59869a80bd..1306f12e88c9e324f587b84a491a4e70517f7360 100644
--- a/content/browser/android/content_view_core_impl.cc
+++ b/content/browser/android/content_view_core_impl.cc
@@ -151,6 +151,7 @@ ContentViewCoreImpl::ContentViewCoreImpl(JNIEnv* env, jobject obj,
       root_layer_(cc::Layer::create()),
       tab_crashed_(false),
       input_events_delivered_at_vsync_(input_events_delivered_at_vsync),
+      has_touch_event_handlers_(false),
       renderer_frame_pending_(false),
       window_android_(window_android) {
   CHECK(web_contents) <<
@@ -498,6 +499,7 @@ void ContentViewCoreImpl::ConfirmTouchEvent(InputEventAckState ack_result) {
 void ContentViewCoreImpl::HasTouchEventHandlers(bool need_touch_events) {
   JNIEnv* env = AttachCurrentThread();
   ScopedJavaLocalRef<jobject> j_obj = java_ref_.get(env);
+  has_touch_event_handlers_ = need_touch_events;
   if (j_obj.is_null())
     return;
   Java_ContentViewCore_hasTouchEventHandlers(env,
@@ -866,11 +868,10 @@ WebGestureEvent ContentViewCoreImpl::MakeGestureEvent(WebInputEvent::Type type,
 
 void ContentViewCoreImpl::UpdateVSyncFlagOnInputEvent(
     WebKit::WebInputEvent* event) const {
-  if (!input_events_delivered_at_vsync_)
+  if (!input_events_delivered_at_vsync_ || has_touch_event_handlers_)
     return;
   if (event->type == WebInputEvent::GestureScrollUpdate ||
-      event->type == WebInputEvent::GesturePinchUpdate ||
-      event->type == WebInputEvent::TouchMove)

[jamesr, 2013/01/16 04:13:26]

whaaaa? why was this here?

actually, this whole function seems kind of like bullshit.  we don't have any
way to tell that we're in this mode from the android framework?

[Sami, 2013/01/16 10:49:15]

From Android's point of view input events are always delivered right before
vsync if we're on JB+, but the problem is that we have at least two different
event queues between the framework and the renderer which affect which events
get sent and when.

Here I'm limiting the vsync bit to those events that are guaranteed to be sent
at the right time -- it doesn't make sense to do it for, e.g., the touch handler
case because the real vsync signal will have reached the renderer by the time we
get an ack from JS.

Maybe it would help if I move this logic to where the events are generated in
Java?

+      event->type == WebInputEvent::GesturePinchUpdate)
     event->modifiers |= WebInputEvent::IsLastInputEventForCurrentVSync;
 }