Attach a WebLayer to a frame element for out-of-process iframes.

Source/core/html/HTMLFrameOwnerElement.h

Index: Source/core/html/HTMLFrameOwnerElement.h
diff --git a/Source/core/html/HTMLFrameOwnerElement.h b/Source/core/html/HTMLFrameOwnerElement.h
index 834ac123c70af030eaf94926ddb244fb900c836b..70a3d71369206d8769917f281ee2063c4d57fb16 100644
--- a/Source/core/html/HTMLFrameOwnerElement.h
+++ b/Source/core/html/HTMLFrameOwnerElement.h
@@ -24,6 +24,10 @@
 #include "core/html/HTMLElement.h"
 #include "wtf/HashCountedSet.h"
 
+namespace blink {
+class WebLayer;
+}
+
 namespace WebCore {
 
 class DOMWindow;
@@ -63,6 +67,9 @@ public:
 
     virtual bool isObjectElement() const { return false; }
 
+    void setPlatformLayer(blink::WebLayer* platformLayer) { m_platformLayer = platformLayer; }
+    blink::WebLayer* platformLayer() const { return m_platformLayer; }
+
 protected:
     HTMLFrameOwnerElement(const QualifiedName& tagName, Document&);
     void setSandboxFlags(SandboxFlags);
@@ -75,6 +82,9 @@ private:
 
     Frame* m_contentFrame;
     SandboxFlags m_sandboxFlags;
+
+    // This layer is for frames whose contents are being renderered in a separate process.
+    blink::WebLayer* m_platformLayer;
 };
 
 DEFINE_NODE_TYPE_CASTS(HTMLFrameOwnerElement, isFrameOwnerElement());