Refactor postMessage for out-of-process iframes.

content/browser/frame_host/render_frame_host_delegate.h

Index: content/browser/frame_host/render_frame_host_delegate.h
diff --git a/content/browser/frame_host/render_frame_host_delegate.h b/content/browser/frame_host/render_frame_host_delegate.h
index 56b563474e07c071f2f250fbf98e4b150b82258f..83233ea2d0183317035323b89d0a98e598fb07f0 100644
--- a/content/browser/frame_host/render_frame_host_delegate.h
+++ b/content/browser/frame_host/render_frame_host_delegate.h
@@ -11,6 +11,7 @@
 #include "base/i18n/rtl.h"
 #include "content/common/content_export.h"
 #include "content/common/frame_message_enums.h"
+#include "content/public/browser/site_instance.h"
 #include "content/public/common/javascript_message_type.h"
 #include "content/public/common/media_stream_request.h"
 #include "net/http/http_response_headers.h"
@@ -168,6 +169,25 @@ class CONTENT_EXPORT RenderFrameHostDelegate {
   // Notification that the frame wants to go out of fullscreen mode.
   virtual void ExitFullscreenMode() {}
 
+  // Let the delegate decide whether postMessage should be delivered to
+  // |target_rfh| from a source frame in the given SiteInstance.
+  virtual bool ShouldRouteMessageEvent(
+      RenderFrameHost* target_rfh,
+      SiteInstance* source_site_instance) const;
+
+  // Ensure that |render_frame_host| has swapped-out RenderViews and proxies
+  // for itself and for each frame on its opener chain in the current frame's
+  // SiteInstance.  Returns the routing ID of the swapped-out RenderView
+  // corresponding to |render_frame_host|.
+  //
+  // TODO(alexmos): This method will be removed once opener tracking and
+  // CreateOpenerRenderViews moves out of WebContents and into lower layers, as
+  // part of https://crbug.com/225940.  Currently, this method temporarily
+  // supports cross-process postMessage in non-site-per-process mode, where we
+  // need to create any missing proxies for the message's source frame and its
+  // opener chain on demand.
+  virtual int EnsureOpenerRenderViewsExist(RenderFrameHost* render_frame_host);

[alexmos, 2015/04/02 23:17:00]

We have a similar method in RFHM::Delegate,
CreateOpenerRenderViewsForRenderManager.  The difference here is that we need to
create swapped-out RVs starting from the current RFH rather than its opener, and
we need to not follow the opener chain for <webview> to match postMessage’s old
behavior.  This method will not be necessary once I clean up the opener stuff,
but in the meantime, do you think something like this is an acceptable
workaround?  I'm not sure whether it’s best to combine this with
CreateOpenerRenderViewsForRenderManager or keep it here, and whether its name
should indicate that it's intended for postMessage only.

[Charlie Reis, 2015/04/06 16:18:55]

Yes, I'm ok with this as a short term way to support swapped out RVs.  No need
to mention postMessage in the name, given the warning that it's going to be
removed.

+
 #if defined(OS_WIN)
   // Returns the frame's parent's NativeViewAccessible.
   virtual gfx::NativeViewAccessible GetParentNativeViewAccessible();