Include control clip in list of clip-related properties.

third_party/WebKit/Source/core/layout/compositing/CompositingLayerAssigner.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingLayerAssigner.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingLayerAssigner.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingLayerAssigner.cpp
index c146c8bbb7cbf6abdb39ed4929975891d8bbe732..3c319fe316da2da386084ecd8bf065db6e15f61f 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingLayerAssigner.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingLayerAssigner.cpp
@@ -133,7 +133,7 @@ CompositingLayerAssigner::getReasonsPreventingSquashing(
   // where a LayoutVideo does not report that it needs to be directly
   // composited.  Video does not currently support sharing a backing, but this
   // could be generalized in the future. The following layout tests fail if we
-  // permit the video to share a backing with other layers.
+  // permit the video to share a backing with other laycers.

[amineer, 2017/03/23 17:30:12]

typo?

   //
   // compositing/video/video-controls-layer-creation.html
   if (layer->layoutObject().isVideo() ||
@@ -173,6 +173,15 @@ CompositingLayerAssigner::getReasonsPreventingSquashing(
   if (layer->scrollParent() && layer->hasCompositingDescendant())
     return SquashingDisallowedReasonScrollChildWithCompositedDescendants;
 
+  // It's possible for this reason to be true but not the above ones. One
+  // example is scrolling input boxes, which do not "scroll" but use
+  // scrolling contents layers to allow typing beyond the input bounds.
+  if ((squashingLayer.getScrollableArea() &&
+       squashingLayer.getScrollableArea()->usesCompositedScrolling()) ||
+      (layer->getScrollableArea() &&
+       layer->getScrollableArea()->usesCompositedScrolling()))
+    return SquashingDisallowedReasonCompositedScrolling;
+
   if (layer->opacityAncestor() != squashingLayer.opacityAncestor())
     return SquashingDisallowedReasonOpacityAncestorMismatch;