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

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 5dfcd1fc6da28f908bcf73e18c992e52aa4cf061..af48069f989421cf8deff8682d098cf68030c8e5 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -1641,6 +1641,9 @@ PassRefPtr<ComputedStyle> Element::styleForLayoutObject()
             style->setHasInlineTransform(inlineStyle->hasProperty(CSSPropertyTransform) || inlineStyle->hasProperty(CSSPropertyWebkitTransform));
     }
 
+    if (hasCompositorProxy())
+        style->setHasCompositorProxy(true);
+
     document().didRecalculateStyleForElement();
     return style.release();
 }