Read compositor VSync information from platform, when possible

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 76e09c4566726506239bd77e6b9fecf25f84a40f..160e2229ea16c0d9bbda46e7a1eef23db78a53e6 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -498,10 +498,20 @@ bool Compositor::HasObserver(CompositorObserver* observer) {
 }
 
 void Compositor::OnUpdateVSyncParameters(base::TimeTicks timebase,
-                                         base::TimeDelta interval) {
-  FOR_EACH_OBSERVER(CompositorObserver,
-                    observer_list_,
-                    OnUpdateVSyncParameters(this, timebase, interval));
+                                         base::TimeDelta interval,
+                                         bool interval_is_authoritative) {
+  if (interval_is_authoritative) {
+    authoritative_vsync_interval_ = interval;
+  } else {
+    if (authoritative_vsync_interval_ != base::TimeDelta())
+      interval = authoritative_vsync_interval_;
+  }
+
+  if (!timebase.is_null()) {
+    FOR_EACH_OBSERVER(CompositorObserver,
+                      observer_list_,
+                      OnUpdateVSyncParameters(this, timebase, interval));
+  }
 }
 
 void Compositor::Layout() {