Bug 1302949 - Skip calling CalculateCumulativeChangeHint; r=heycam

There are a few pieces missing before we can do this with Servo. Since this
only enables an optimization for off-screen animations we should skip this
for now so it doesn't block animations from running.

MozReview-Commit-ID: GecHWQZYxpK

--HG--
extra : rebase_source : c0330b104afb4b970569c0cb650315e633b7e796
extra : histedit_source : db91b37d3370c9b766976b42b0701f6e0ec56159

dom/animation/KeyframeEffectReadOnly.cpp

@@ -296,7 +296,10 @@ KeyframeEffectReadOnly::UpdateProperties(nsStyleContext* aStyleContext)
       runningOnCompositorProperties.HasProperty(property.mProperty);
   }
 
-  CalculateCumulativeChangeHint(aStyleContext);
+  // FIXME (bug 1303235): Do this for Servo too
+  if (aStyleContext->PresContext()->StyleSet()->IsGecko()) {
+    CalculateCumulativeChangeHint(aStyleContext);
+  }
 
   MarkCascadeNeedsUpdate();
 
@@ -1275,6 +1278,13 @@ KeyframeEffectReadOnly::CanIgnoreIfNotVisible() const
     return false;
   }
 
+  // FIXME (bug 1303235): We don't calculate mCumulativeChangeHint for
+  // the Servo backend yet
+  nsPresContext* presContext = GetPresContext();
+  if (!presContext || presContext->StyleSet()->IsServo()) {
+    return false;
+  }
+
   // FIXME: For further sophisticated optimization we need to check
   // change hint on the segment corresponding to computedTiming.progress.
   return NS_IsHintSubset(