Make <webview> use out-of-process iframe architecture.

content/public/browser/web_contents.h

Index: content/public/browser/web_contents.h
diff --git a/content/public/browser/web_contents.h b/content/public/browser/web_contents.h
index b2eaf32ca3591147d42a067bc6722d402f00fb66..ab0fe6df66aa4ccdd768fadbc80f9ab85b6bcb0a 100644
--- a/content/public/browser/web_contents.h
+++ b/content/public/browser/web_contents.h
@@ -386,6 +386,12 @@ class WebContents : public PageNavigator,
   // has one.
   virtual void DispatchBeforeUnload(bool for_cross_site_transition) = 0;
 
+  // Attaches this inner WebContents to its container frame
+  // |outer_contents_frame| in |outer_web_contents|.
+  virtual void AttachToOuterWebContentsFrame(
+      WebContents* outer_web_contents,
+      RenderFrameHost* outer_contents_frame) = 0;
+
   // Commands ------------------------------------------------------------------
 
   // Stop any pending navigation.