scheduler: Reset gesture state at start of a mouse drag

third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc

Index: third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
index 9c5e33a261fef355db3ff3399cc626aa9141ce70..6c32dcbc496d95397d821085935c2d5cccc7f4a3 100644
--- a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
+++ b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
@@ -468,7 +468,8 @@ bool RendererSchedulerImpl::ShouldPrioritizeInputEvent(
     const blink::WebInputEvent& web_input_event) {
   // We regard MouseMove events with the left mouse button down as a signal
   // that the user is doing something requiring a smooth frame rate.
-  if (web_input_event.type == blink::WebInputEvent::MouseMove &&
+  if ((web_input_event.type == blink::WebInputEvent::MouseDown ||

[alex clarke (OOO till 29th), 2016/08/22 11:30:09]

Are we going to start blocking expensive tasks if the user clicks on something? 
Which ever way is decided, please add a test to lock in the behavior.

[Sami, 2016/08/22 13:25:14]

Right, we wouldn't want to do blocking based on a click. I've added a test.
Basically a mouse click now means main thread input handling, which can
prioritize compositing but won't block anything.

+       web_input_event.type == blink::WebInputEvent::MouseMove) &&
       (web_input_event.modifiers & blink::WebInputEvent::LeftButtonDown)) {
     return true;
   }
@@ -528,7 +529,7 @@ void RendererSchedulerImpl::UpdateForInputEventOnCompositorThread(
   if (input_event_state == InputEventState::EVENT_CONSUMED_BY_COMPOSITOR)
     AnyThread().user_model.DidFinishProcessingInputEvent(now);
 
-  if (type) {
+  if (type != blink::WebInputEvent::Undefined) {

[alex clarke (OOO till 29th), 2016/08/22 11:30:09]

Perhaps handle this as a case in the switch?

[Sami, 2016/08/22 13:25:15]

Good idea -- makes more sense that way.

     switch (type) {
       case blink::WebInputEvent::TouchStart:
         AnyThread().awaiting_touch_start_response = true;
@@ -576,6 +577,20 @@ void RendererSchedulerImpl::UpdateForInputEventOnCompositorThread(
         // meaningful touchstart response and should not impact task priority.
         break;
 
+      case blink::WebInputEvent::MouseDown:
+        // Reset tracking state at the start of a new mouse drag gesture.
+        AnyThread().last_gesture_was_compositor_driven = false;
+        AnyThread().default_gesture_prevented = true;
+        break;
+
+      case blink::WebInputEvent::MouseMove:
+        // Consider mouse movement with the left button held down (see
+        // ShouldPrioritizeInputEvent) similarly to a touch gesture.
+        AnyThread().last_gesture_was_compositor_driven =
+            input_event_state == InputEventState::EVENT_CONSUMED_BY_COMPOSITOR;
+        AnyThread().awaiting_touch_start_response = false;
+        break;
+
       default:
         AnyThread().awaiting_touch_start_response = false;
         break;
@@ -1019,8 +1034,6 @@ RendererSchedulerImpl::UseCase RendererSchedulerImpl::ComputeCurrentUseCase(
     //    stream of input events and has prevented a default gesture from being
     //    started.
     // 4. SYNCHRONIZED_GESTURE where the gesture is processed on both threads.
-    // TODO(skyostil): Consider removing in_idle_period_ and
-    // HadAnIdlePeriodRecently() unless we need them here.
     if (AnyThread().last_gesture_was_compositor_driven) {
       if (AnyThread().begin_main_frame_on_critical_path) {
         return UseCase::SYNCHRONIZED_GESTURE;
@@ -1281,12 +1294,6 @@ void RendererSchedulerImpl::OnNavigationStarted() {
   ResetForNavigationLocked();
 }
 
-bool RendererSchedulerImpl::HadAnIdlePeriodRecently(base::TimeTicks now) const {
-  return (now - AnyThread().last_idle_period_end_time) <=
-         base::TimeDelta::FromMilliseconds(
-             kIdlePeriodStarvationThresholdMillis);
-}
-
 void RendererSchedulerImpl::SuspendTimerQueueWhenBackgrounded() {
   DCHECK(MainThreadOnly().renderer_backgrounded);
   if (MainThreadOnly().timer_queue_suspended_when_backgrounded)