Use estimated vsync period on Android

ui/android/java/src/org/chromium/ui/VSyncMonitor.java

Index: ui/android/java/src/org/chromium/ui/VSyncMonitor.java
diff --git a/ui/android/java/src/org/chromium/ui/VSyncMonitor.java b/ui/android/java/src/org/chromium/ui/VSyncMonitor.java
index af8f87b5ffd898c832a1fa2f0db7cd590e50ca89..9c421aa14546db038c7530c5c963b236d9ce68de 100644
--- a/ui/android/java/src/org/chromium/ui/VSyncMonitor.java
+++ b/ui/android/java/src/org/chromium/ui/VSyncMonitor.java
@@ -24,7 +24,10 @@ public class VSyncMonitor {
     private static final long NANOSECONDS_PER_MILLISECOND = 1000000;
     private static final long NANOSECONDS_PER_MICROSECOND = 1000;
 
+    private static final long MAX_VALID_VSYNC_PERIOD_NANOSECONDS = NANOSECONDS_PER_SECOND / 30;
+
     private boolean mInsideVSync = false;
+    private boolean mConsecutiveVSync = false;
 
     /**
      * VSync listener class
@@ -41,7 +44,7 @@ public class VSyncMonitor {
     private Listener mListener;
 
     // Display refresh rate as reported by the system.
-    private final long mRefreshPeriodNano;
+    private long mRefreshPeriodNano;
 
     private boolean mHaveRequestInFlight;
 
@@ -85,10 +88,22 @@ public class VSyncMonitor {
         if (enableJBVSync && Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
             // Use Choreographer on JB+ to get notified of vsync.
             mChoreographer = Choreographer.getInstance();
+            final boolean useEstimatedRefreshPeriod =
+                mRefreshPeriodNano > MAX_VALID_VSYNC_PERIOD_NANOSECONDS;

[Sami, 2014/10/02 15:52:31]

Indent by +4 spaces.

             mVSyncFrameCallback = new Choreographer.FrameCallback() {
                 @Override
                 public void doFrame(long frameTimeNanos) {
                     TraceEvent.begin("VSync");
+                    if (useEstimatedRefreshPeriod && mConsecutiveVSync) {
+                        // Display.getRefreshRate() is unreliable on some platforms.
+                        // Adjust refresh period- initial value is based on Display.getRefreshRate()
+                        // after that it asymptotically approaches the real value.
+                        long lastRefreshDurationNano = frameTimeNanos - mGoodStartingPointNano;
+                        float lastRefreshDurationWeight = 0.75;
+                        mRefreshPeriodNano = (long) (

[Sami, 2014/10/02 15:52:31]

nit: This would be slightly more efficient as:

  mRefreshPeriodNano += (long)(lastRefreshDurationWeight *
(lastRefreshDurationNano - mRefreshPeriodNano));

+                            mRefreshPeriodNano * (1.0f - lastRefreshDurationWeight) +
+                            lastRefreshDurationNano * lastRefreshDurationWeight);
+                    }
                     mGoodStartingPointNano = frameTimeNanos;
                     onVSyncCallback(frameTimeNanos, getCurrentNanoTime());
                     TraceEvent.end("VSync");
@@ -186,6 +201,7 @@ public class VSyncMonitor {
         mHaveRequestInFlight = true;
         if (postSyntheticVSync()) return;
         if (isVSyncSignalAvailable()) {
+            mConsecutiveVSync = mInsideVSync;

[Sami, 2014/10/02 15:52:31]

This can have some false negatives if the next frame is requested from outside
the vsync callback, but I don't think that will generally be a problem.

             mChoreographer.postFrameCallback(mVSyncFrameCallback);
         } else {
             postRunnableCallback();