Bug 1707044 - Remove invalid assert in AnimationFrameRecyclingQueue::RecycleFrame. r=tnikkel

The assert in question is overly conservative. The dirty rects may be
calculated using a more conservative estimate of the whole frame, and
after the animation has completed its first pass, we may have determined
that it is unnecessarily too large and shrink it accordingly. There may
still be frames lingering with the old larger rect however, and trip
this assert falsely.

Differential Revision: https://phabricator.services.mozilla.com/D113155

image/AnimationFrameBuffer.cpp

@@ -408,8 +408,11 @@ RawAccessFrameRef AnimationFrameRecyclingQueue::RecycleFrame(
     // area. We know that all of the frames still in the recycling queue
     // need to take into account the same dirty rect because they are also
     // frames which cross the boundary.
+    //
+    // Note that this may actually shrink the dirty rect if we estimated it
+    // earlier with the full frame size and now we have the actual, more
+    // conservative aggregate for the animation.
     for (RecycleEntry& entry : mRecycle) {
-      MOZ_ASSERT(mFirstFrameRefreshArea.Contains(entry.mDirtyRect));
       entry.mDirtyRect = mFirstFrameRefreshArea;
     }
     // Until we advance to the first frame again, any subsequent recycled