compositor-worker: Force elements to grow a layer when a CompositorProxy is created.

Source/core/layout/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/layout/compositing/CompositingReasonFinder.h"
 
 #include "core/CSSPropertyNames.h"
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
@@ skipping 92 matching lines @@
 
     if (style.hasPerspective())
         reasons |= CompositingReasonPerspectiveWith3DDescendants;
 
     // Ignore scroll-blocks-on on the document element, because it will get propagated to
     // the LayoutView (by Document::inheritHtmlAndBodyElementStyles) and we don't want to
     // create two composited layers.
     if (style.hasScrollBlocksOn() && !renderer->isDocumentElement())
         reasons |= CompositingReasonScrollBlocksOn;
 
+    if (style.hasCompositorProxy())
+        reasons |= CompositingReasonCompositorProxy;
+
     // If the implementation of createsGroup changes, we need to be aware of that in this part of code.
     ASSERT((renderer->isTransparent() || renderer->hasMask() || renderer->hasFilter() || style.hasBlendMode()) == renderer->createsGroup());
 
     if (style.hasMask())
         reasons |= CompositingReasonMaskWithCompositedDescendants;
 
     if (style.hasFilter())
         reasons |= CompositingReasonFilterWithCompositedDescendants;
 
     // See Layer::updateTransform for an explanation of why we check both.
@@ skipping 104 matching lines @@
             // Either way, we don't need to require compositing for scroll blocks on.  This avoids
             // enabling compositing by default, and avoids cluttering the root layers compositing reasons.
             return false;
         }
     }
 
     return true;
 }
 
 }