Move fallback tick handling to compositor thread

content/renderer/android/synchronous_compositor_output_surface.cc

Index: content/renderer/android/synchronous_compositor_output_surface.cc
diff --git a/content/renderer/android/synchronous_compositor_output_surface.cc b/content/renderer/android/synchronous_compositor_output_surface.cc
index cb41202d297b3d3d620b1d1745c280167cda0c5c..c5dcb2caf8fcf370c7c69cba0bd60c99498cc02a 100644
--- a/content/renderer/android/synchronous_compositor_output_surface.cc
+++ b/content/renderer/android/synchronous_compositor_output_surface.cc
@@ -26,6 +26,8 @@ namespace content {
 
 namespace {
 
+const int64_t kFallbackTickTimeoutInMilliseconds = 100;
+
 // Do not limit number of resources, so use an unrealistically high value.
 const size_t kNumResourcesLimit = 10 * 1000 * 1000;
 
@@ -132,10 +134,27 @@ void SynchronousCompositorOutputSurface::SwapBuffers(
   did_swap_ = true;
 }
 
+void SynchronousCompositorOutputSurface::FallbackTickFired() {

[boliu, 2016/03/11 17:43:09]

DCHECK(CalledOnValidThread());

[Tobias Sargeant, 2016/03/14 13:11:03]

Done.

+  TRACE_EVENT0("android_webview",

[boliu, 2016/03/11 17:43:09]

change category to "renderer"

[Tobias Sargeant, 2016/03/14 13:11:03]

Done.

+               "SynchronousCompositorOutputSurface::FallbackTickFired");
+  SkBitmap bitmap;
+  bitmap.allocN32Pixels(1, 1);
+  bitmap.eraseColor(0);
+  SkCanvas canvas(bitmap);
+  DemandDrawSw(&canvas);
+}
+
 void SynchronousCompositorOutputSurface::Invalidate() {
   DCHECK(CalledOnValidThread());
   if (sync_client_)
     sync_client_->Invalidate();
+
+  fallback_tick_.Reset(

[boliu, 2016/03/11 17:43:09]

Need to check if fallback tick is already pending, so this doesn't end up in a
live lock where compositor calls invalidate more frequently than ticks, so it
gets pushed back indefinitely.

[Tobias Sargeant, 2016/03/14 13:11:03]

Done.

+      base::Bind(&SynchronousCompositorOutputSurface::FallbackTickFired,
+                 base::Unretained(this)));
+  base::MessageLoop::current()->PostDelayedTask(
+      FROM_HERE, fallback_tick_.callback(),
+      base::TimeDelta::FromMilliseconds(kFallbackTickTimeoutInMilliseconds));
 }
 
 void SynchronousCompositorOutputSurface::DemandDrawHw(
@@ -148,6 +167,7 @@ void SynchronousCompositorOutputSurface::DemandDrawHw(
   DCHECK(CalledOnValidThread());
   DCHECK(HasClient());
   DCHECK(context_provider_.get());
+  fallback_tick_.Cancel();
 
   surface_size_ = surface_size;
   client_->SetExternalTilePriorityConstraints(viewport_rect_for_tile_priority,
@@ -160,6 +180,7 @@ void SynchronousCompositorOutputSurface::DemandDrawSw(SkCanvas* canvas) {
   DCHECK(CalledOnValidThread());
   DCHECK(canvas);
   DCHECK(!current_sw_canvas_);
+  fallback_tick_.Cancel();
 
   base::AutoReset<SkCanvas*> canvas_resetter(&current_sw_canvas_, canvas);