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

Source/platform/graphics/CompositingReasons.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 "platform/graphics/CompositingReasons.h"
 
 #include "wtf/StdLibExtras.h"
 
 namespace blink {
@@ skipping 40 matching lines @@
         "Has clipping ancestor" },
     { CompositingReasonVideoOverlay,
         "videoOverlay",
         "Is overlay controls for video" },
     { CompositingReasonWillChangeCompositingHint,
         "willChange",
         "Has a will-change compositing hint" },
     { CompositingReasonScrollBlocksOn,
         "scrollBlocksOn",
         "Has a CSS scroll-blocks-on value other than none" },
+    { CompositingReasonCompositorProxy,
+        "compositorProxy",
+        "Has a CompositorProxy object" },
     { CompositingReasonAssumedOverlap,
         "assumedOverlap",
         "Might overlap other composited content" },
     { CompositingReasonOverlap,
         "overlap",
         "Overlaps other composited content" },
     { CompositingReasonNegativeZIndexChildren,
         "negativeZIndexChildren",
         "Parent with composited negative z-index content" },
     { CompositingReasonScrollsWithRespectToSquashingLayer,
@@ skipping 120 matching lines @@
         "layerForScrollingBlockSelection",
         "Secondary layer, to house block selection gaps for composited scrolling with no scrolling contents" },
     { CompositingReasonInlineTransform,
         "inlineTransform",
         "Has an inline transform, which causes subsequent layers to assume overlap" },
 };
 
 size_t kNumberOfCompositingReasons = WTF_ARRAY_LENGTH(kCompositingReasonStringMap);
 
 } // namespace blink