Scheduler: Switch from high to low latency mode if possible.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 93b91311e6e94c9f821ad8753cbe56d40d6b27b4..868df6eddcaffa1afd3c5e153f4d0c9d3249456c 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -184,6 +184,12 @@ void Scheduler::BeginImplFrame(const BeginFrameArgs& args) {
   last_begin_impl_frame_args_ = args;
   last_begin_impl_frame_args_.deadline -= client_->DrawDurationEstimate();
   state_machine_.OnBeginImplFrame(last_begin_impl_frame_args_);
+
+  if (settings_.switch_to_low_latency_if_possible) {
+    state_machine_.SetSkipBeginMainFrameToReduceLatency(
+        state_machine_.InHighLatencyMode() && CanOperateInLowLatencyMode());
+  }
+
   ProcessScheduledActions();
 
   if (!state_machine_.HasInitializedOutputSurface())
@@ -344,4 +350,15 @@ bool Scheduler::WillDrawIfNeeded() const {
   return !state_machine_.PendingDrawsShouldBeAborted();
 }
 
+bool Scheduler::CanOperateInLowLatencyMode() const {
+  // If the main thread computation and commit can be finished before the
+  // deadline we can operate in low latency mode.
+  base::TimeTicks estimated_draw_time =
+      last_begin_impl_frame_args_.frame_time +
+      client_->BeginMainFrameToCommitDurationEstimate() +
+      client_->CommitToActivateDurationEstimate();
+
+  return estimated_draw_time < last_begin_impl_frame_args_.deadline;
+}
+
 }  // namespace cc