Web Animations CSS: Fixing startDelay for compositor translation.

Source/core/animation/CompositorAnimations.cpp

Index: Source/core/animation/CompositorAnimations.cpp
diff --git a/Source/core/animation/CompositorAnimations.cpp b/Source/core/animation/CompositorAnimations.cpp
index 0b76bccf0e111b50f59ab65b6bc6b01d83f8b27b..0406bb2ad220def7fd7eb97e287cf40359de8aa4 100644
--- a/Source/core/animation/CompositorAnimations.cpp
+++ b/Source/core/animation/CompositorAnimations.cpp
@@ -357,8 +357,9 @@ bool CompositorAnimationsImpl::convertTimingForCompositor(const Timing& timing,
         ASSERT(out.adjustedIterationCount > 0);
     }
 
-    out.scaledTimeOffset = scaledStartDelay + skippedIterations * out.scaledDuration;
-    ASSERT(out.scaledTimeOffset <= 0);
+    // Compositor's time offset is positive for seeking into the animation.
+    out.scaledTimeOffset = -(scaledStartDelay + skippedIterations * out.scaledDuration);
+    ASSERT(out.scaledTimeOffset >= 0);
     return true;
 }