Defer starting of animations until after compositing update

Source/core/animation/AnimationClock.h

Index: Source/core/animation/AnimationClock.h
diff --git a/Source/core/animation/AnimationClock.h b/Source/core/animation/AnimationClock.h
index f6a2cdb84991f6777818a1f67bf251d269e1b757..0d2545e487c448f44bd71b189ec1c87ca7605ffc 100644
--- a/Source/core/animation/AnimationClock.h
+++ b/Source/core/animation/AnimationClock.h
@@ -34,6 +34,17 @@
 #include "wtf/CurrentTime.h"
 #include "wtf/PassOwnPtr.h"
 
+namespace {

[abarth-chromium, 2014/02/20 17:52:00]

Please don't use anonymous namespaces in headers.  That makes the linker go
crazy.

[dstockwell, 2014/02/24 06:03:25]

Done.

+
+// FIXME: This value is used to suppress updates when time is required outside of a frame.
+// The purpose of allowing the clock to update during such periods is to allow animations
+// to have an appropriate start time and for getComputedStyle to attempt to catch-up to a
+// compositor animation. However a more accurate system might be to attempt to phase-lock
+// with the frame clock.
+const double minTimeBeforeUnsynchronizedTick = 0.005;
+
+}
+
 namespace WebCore {
 
 class AnimationClock {
@@ -52,8 +63,11 @@ public:
 
     double currentTime()
     {
-        if (!m_frozen)
-            updateTime(m_monotonicallyIncreasingTime());
+        if (!m_frozen) {
+            double newTime = m_monotonicallyIncreasingTime();
+            if (newTime >= m_time + minTimeBeforeUnsynchronizedTick)
+                m_time = newTime;
+        }
         return m_time;
     }