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 2993d8a6fd21dffc40465c2ed46af07f0fba6a30..45d40c78f3b8f9c5bb1e9258735d4b73cdc143c5 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -446,10 +446,20 @@ 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() {