Animation: Composite animations with any start delay specified

Source/core/animation/CompositorAnimationsImpl.h

Index: Source/core/animation/CompositorAnimationsImpl.h
diff --git a/Source/core/animation/CompositorAnimationsImpl.h b/Source/core/animation/CompositorAnimationsImpl.h
index e91a8760be6bc4f04d16e4c93b9a6db279c3231b..05e87b974e3a006a5f7db54483b76c2b3b821b5b 100644
--- a/Source/core/animation/CompositorAnimationsImpl.h
+++ b/Source/core/animation/CompositorAnimationsImpl.h
@@ -41,6 +41,15 @@ class WebCompositorAnimationCurve;
 class CompositorAnimationsImpl {
 private:
     struct CompositorTiming {
+        void assertValid() const
+        {
+            ASSERT(scaledDuration > 0);
+            ASSERT(std::isfinite(scaledTimeOffset));
+            ASSERT(adjustedIterationCount > 0 || adjustedIterationCount == -1);
+            ASSERT(std::isfinite(playbackRate) && playbackRate);
+            ASSERT(iterationStart >= 0);
+        }
+
         Timing::PlaybackDirection direction;
         double scaledDuration;
         double scaledTimeOffset;