Retry tree activation if raster tasks finish during first half of vsync interval

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 3cc54e64b5524c134e4f3232982201e5925e1b1b..deccf0eb4ff62a36faedaa26c0e8fb8201c6de74 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -28,6 +28,10 @@ const double kContextRecreationTickRate = 0.03;
 // Measured in seconds.
 const double kSmoothnessTakesPriorityExpirationDelay = 0.25;
 
+// Time period in seconds from the previous vsync during which we are allowed to
+// retry tree activation and rendering.
+const double kTreeActivationGracePeriod = 0.008;
+
 }  // namespace
 
 namespace cc {
@@ -849,6 +853,21 @@ void ThreadProxy::ScheduledActionActivatePendingTreeIfNeeded() {
   layer_tree_host_impl_->ActivatePendingTreeIfNeeded();
 }
 
+void ThreadProxy::DidFinishTileRasterTasks() {
+  DCHECK(IsImplThread());
+  TRACE_EVENT0("cc", "LayerTreeHostImpl::DidFinishTileRasterTasks");
+  base::TimeDelta time_since_vsync =
+      base::TimeTicks::Now() - scheduler_on_impl_thread_->LastVSyncTime();
+  base::TimeDelta grace_period =
+      base::TimeDelta::FromMilliseconds(kTreeActivationGracePeriod);
+  if (time_since_vsync > grace_period) {
+    TRACE_EVENT0("cc", "LayerTreeHostImpl::DidFinishTileRasterTasks: too late");
+    return;
+  }
+  if (layer_tree_host_impl_->ActivatePendingTreeIfNeeded())
+    scheduler_on_impl_thread_->VSyncTick(false);
+}
+
 void ThreadProxy::ScheduledActionBeginContextRecreation() {
   DCHECK(IsImplThread());
   Proxy::MainThread()->PostTask(