Adds BeginFrameControl via DevTools.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 14d5e69e6a0b6521be64398bb0755aca1ce5e559..622b88524d0bd0559e6406a41ced1e3e479f7708 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -396,6 +396,9 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
     return;
   }
 
+  state_machine_.SetBeginFrameAllowsLatencyOptimizations(
+      adjusted_args.allow_latency_optimizations);
+
   BeginImplFrame(adjusted_args);
 }
 
@@ -696,6 +699,10 @@ bool Scheduler::ShouldRecoverMainLatency(
   if (state_machine_.ImplLatencyTakesPriority())
     return false;
 
+  // If the args explicitly forbid it, we shouldn't skip BeginMainFrames.
+  if (!args.allow_latency_optimizations)
+    return false;
+
   return can_activate_before_deadline;
 }
 
@@ -719,6 +726,10 @@ bool Scheduler::ShouldRecoverImplLatency(
   if (!impl_thread_is_likely_high_latency)
     return false;
 
+  // If the args explicitly forbid it, we shouldn't skip BeginFrames.
+  if (!args.allow_latency_optimizations)
+    return false;
+
   // The deadline may be in the past if our draw time is too long.
   bool can_draw_before_deadline = args.frame_time < args.deadline;