Android WebView: flush input events during onVSync

content/browser/renderer_host/render_widget_host_view_android.cc

Index: content/browser/renderer_host/render_widget_host_view_android.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_android.cc b/content/browser/renderer_host/render_widget_host_view_android.cc
index dd65887f78db5d47ad01b2adc5b5da168d243a18..65cc2601e8934012d36b8ee7f8636a9ca7d0364a 100644
--- a/content/browser/renderer_host/render_widget_host_view_android.cc
+++ b/content/browser/renderer_host/render_widget_host_view_android.cc
@@ -1304,6 +1304,12 @@ void RenderWidgetHostViewAndroid::OnSetNeedsFlushInput() {
     return;
   TRACE_EVENT0("input", "RenderWidgetHostViewAndroid::OnSetNeedsFlushInput");
   flush_input_requested_ = true;
+
+  if (!observing_root_window_) {
+    content_view_core_->GetWindowAndroid()->AddObserver(this);

[no sievers, 2014/08/21 18:01:22]

Actually I'm not sure if this is a good idea, since it potentially breaks the
balancing of Add/Remove.

I think Jared's patch takes care of this in a better way by remembering we need
a 'vsync for flush' and requesting it when we become attached to a CVC or
visible.

[boliu, 2014/08/21 18:04:56]

Jared's patch came from this. And we should submit this first, and the clean up
after, since we might want to get this into webvew

I don't think there's a balancing problem here. It should only apply to webview
where we *don't* add observer in attach/visible.

[no sievers, 2014/08/21 18:11:00]

What if OnSetNeedsFlushInput() gets called in Chrome when the view is hidden? I
don't think this method should change the attachment state wrt to the window.

Unfortunately dealing with lifetime issues between CVC, RWHV and WindowAndroid
has previously cost us way too much time, so I'd be careful.

[boliu, 2014/08/21 18:22:52]

Hmm...webview should do what chrome does, which means not flush if it's hidden.
But webview is never hidden.

So instead of adding flush_input_requested_/using_synchronous_compositor_ checks
in show/hide/attach/detach, we can just add " && using_synchronous_compositor_"
here to avoid churn...

Yeah still kinda sucks

+    observing_root_window_ = true;
+  }
+
   content_view_core_->GetWindowAndroid()->RequestVSyncUpdate();
 }
 
@@ -1529,6 +1535,9 @@ void RenderWidgetHostViewAndroid::OnVSync(base::TimeTicks frame_time,
     host_->FlushInput();
   }
 
+  if (using_synchronous_compositor_)
+    return;
+
   TRACE_EVENT0("cc", "RenderWidgetHostViewAndroid::SendBeginFrame");
   base::TimeTicks display_time = frame_time + vsync_period;