Bug 1430884 - Throttle animations producing nsChangeHint_UpdateOverflow change hint if the target element is not visible. r=birtles

In the case where the target element is scrolled out or visibility:hidden and
has no visible descendants, we can treat nsChangeHint_UpdateOverflow just like
transform animations which produce nsChangeHint_UpdatePostTransformOverflow,
i.e. unthrottle the animations periodically if the target element is inside a
scrollable element.  Some transform animations produce UpdateOverflow hint,
so it would be really nice to optimize the hint.

MozReview-Commit-ID: E1MgPZRi8mW

--HG--
extra : rebase_source : d29a29e137742f88a64b3b18a5a7d4e64e76f54f

dom/animation/KeyframeEffect.h

@@ -446,8 +446,9 @@ private:
   // observers reflected by the transform.
   bool HasPropertiesThatMightAffectOverflow() const
   {
-    return mCumulativeChangeHint & (nsChangeHint_UpdatePostTransformOverflow |
-                                    nsChangeHint_AddOrRemoveTransform |
+    return mCumulativeChangeHint & (nsChangeHint_AddOrRemoveTransform |
+                                    nsChangeHint_UpdateOverflow |
+                                    nsChangeHint_UpdatePostTransformOverflow |
                                     nsChangeHint_UpdateTransformLayer);
   }
 

dom/animation/test/mozilla/file_restyles.html

@@ -134,6 +134,7 @@ function waitForWheelEvent(aTarget) {
 
 const omtaEnabled = isOMTAEnabled();
 
+const isAndroid = !!navigator.userAgent.includes("Android");
 const isWebRender =
   SpecialPowers.DOMWindowUtils.layerManagerType == 'WebRender';
 
@@ -1731,6 +1732,30 @@ waitForAllPaints(() => {
     await ensureElementRemoval(div);
   });
 
+  add_task(async function restyling_outline_offset_animations_on_invisible_element() {
+    if (isAndroid) {
+      // FIXME: Bug 1470798: Enable this test on Android.
+      return;
+    }
+    const div = addDiv(null,
+                       { style: 'visibility: hidden; ' +
+                                'outline-style: solid; ' +
+                                'outline-width: 1px;' });
+    const animation =
+      div.animate({ outlineOffset: [ '0px', '10px' ] },
+                  { duration: 100 * MS_PER_SEC,
+                    iterations: Infinity });
+
+    await waitForAnimationReadyToRestyle(animation);
+
+    const markers = await observeStyling(5);
+
+    is(markers.length, 0,
+       'Outline offset animation running on the main-thread on invisible ' +
+       'element should be throttled');
+    await ensureElementRemoval(div);
+  });
+
 });
 
 </script>

layout/base/nsChangeHint.h

@@ -461,6 +461,7 @@ static_assert(!(nsChangeHint_Hints_AlwaysHandledForDescendants &
                nsChangeHint_NeutralChange |                \
                nsChangeHint_UpdateOpacityLayer |           \
                nsChangeHint_AddOrRemoveTransform |         \
+               nsChangeHint_UpdateOverflow |               \
                nsChangeHint_UpdatePostTransformOverflow  | \
                nsChangeHint_UpdateTransformLayer |         \
                nsChangeHint_UpdateUsesOpacity |            \