Adds support for calling postMessage on a frame living in a different renderer.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index cf1ae7891770f99148e58f7b0123f7dac14b31c5..3a2ae6a88f93c0d3399edd62b55a9b68c57b9fca 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -874,6 +874,7 @@ bool RenderViewHostImpl::OnMessageReceived(const IPC::Message& msg) {
                         OnMsgDidChangeNumWheelEvents)
     IPC_MESSAGE_HANDLER(ViewHostMsg_RouteCloseEvent,
                         OnMsgRouteCloseEvent)
+    IPC_MESSAGE_HANDLER(ViewHostMsg_RouteMessageEvent, OnMsgRouteMessageEvent)
     IPC_MESSAGE_HANDLER_DELAY_REPLY(ViewHostMsg_RunJavaScriptMessage,
                                     OnMsgRunJavaScriptMessage)
     IPC_MESSAGE_HANDLER_DELAY_REPLY(ViewHostMsg_RunBeforeUnloadConfirm,
@@ -1263,6 +1264,12 @@ void RenderViewHostImpl::OnMsgRouteCloseEvent() {
   delegate_->RouteCloseEvent(this);
 }
 
+void RenderViewHostImpl::OnMsgRouteMessageEvent(
+    const ViewHostMsg_PostMessage_Params& params) {
+  // Give to the delegate to route to the active RenderViewHost.
+  delegate_->RouteMessageEvent(this, params);

[jam, 2012/05/14 06:41:45]

a while back, I had gone through and removed all the message handlers in RVH
that just call WebContents. just dispatch this message there directly 

[Charlie Reis, 2012/05/14 17:38:43]

It's unsafe to dispatch messages like this directly to WebContents, because we
need to know exactly which RenderViewHost sent the message (hence passing
"this").  Otherwise we end up with bugs like http://crbug.com/126160.

+}
+
 void RenderViewHostImpl::OnMsgRunJavaScriptMessage(
     const string16& message,
     const string16& default_prompt,