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..6f3beafdbe22b5b429de879c02afa408cd28676c 100644
--- a/ui/android/java/src/org/chromium/ui/VSyncMonitor.java
+++ b/ui/android/java/src/org/chromium/ui/VSyncMonitor.java
@@ -24,6 +24,8 @@ public class VSyncMonitor {
     private static final long NANOSECONDS_PER_MILLISECOND = 1000000;
     private static final long NANOSECONDS_PER_MICROSECOND = 1000;
 
+    private static final long PERIOD_THRESHOLD_NANOSECONDS = NANOSECONDS_PER_SECOND / 30;

[Sami, 2014/10/01 11:42:49]

nit: Maybe call this something like MAX_VALID_VSYNC_PERIOD_NANOSECONDS to make
it more obvious what it is for.

+
     private boolean mInsideVSync = false;
 
     /**
@@ -41,7 +43,7 @@ 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 +87,21 @@ 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 > PERIOD_THRESHOLD_NANOSECONDS;
             mVSyncFrameCallback = new Choreographer.FrameCallback() {
                 @Override
                 public void doFrame(long frameTimeNanos) {
                     TraceEvent.begin("VSync");
+                    if (useEstimatedRefreshPeriod) {
+                        // 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;
+                        if (lastRefreshDurationNano <= PERIOD_THRESHOLD_NANOSECONDS) {
+                            mRefreshPeriodNano = (mRefreshPeriodNano + lastRefreshDurationNano) / 2;
+                        }
+                    }
                     mGoodStartingPointNano = frameTimeNanos;
                     onVSyncCallback(frameTimeNanos, getCurrentNanoTime());
                     TraceEvent.end("VSync");
@@ -132,7 +145,7 @@ public class VSyncMonitor {
     /**
      * Determine whether a true vsync signal is available on this platform.
      */
-    private boolean isVSyncSignalAvailable() {
+    public boolean isVSyncSignalAvailable() {

[Sami, 2014/10/01 11:42:49]

Not needed?

         return mChoreographer != null;
     }