Browser Plugin: Implement BrowserPluginObserver.

content/common/browser_plugin_messages.h

Index: content/common/browser_plugin_messages.h
diff --git a/content/common/browser_plugin_messages.h b/content/common/browser_plugin_messages.h
index bd9c98787106d5679c8f3e80d4c356dbc5c93e2a..a181569aceac12464c219e9954ad23d0de6e2cf4 100644
--- a/content/common/browser_plugin_messages.h
+++ b/content/common/browser_plugin_messages.h
@@ -132,6 +132,12 @@ IPC_STRUCT_END()
 IPC_MESSAGE_ROUTED1(BrowserPluginHostMsg_AllocateInstanceID,
                     int /* request_id */)
 
+// Used by the embedder process to forward messages to
+// BrowserPluginGuestObservers.

[Charlie Reis, 2013/02/28 02:12:03]

I'm not sure if this is ok from a security perspective, but I suppose you'll
need a security reviewer for this file anyway.

Why do you need to forward an entire IPC message?  What's an example?

[Fady Samuel, 2013/02/28 22:56:21]

See https://chromiumcodereview.appspot.com/12326168/

This idea was suggested to me by John. I believe this is done elsewhere in the
code. This hides the notion of instance ID from the chrome layer and
BrowserPluginObserver. Messages automagically get to the right place without
needing to know anything about how they're routed there. 

+IPC_MESSAGE_ROUTED2(BrowserPluginHostMsg_ForwardMessage,
+                    int /* instance_id */,
+                    IPC::Message /* message */)
+
 // This message is sent to the browser process to enable or disable autosize
 // mode.
 IPC_MESSAGE_ROUTED3(
@@ -256,6 +262,11 @@ IPC_MESSAGE_ROUTED2(BrowserPluginMsg_AllocateInstanceID_ACK,
                     int /* request_id */,
                     int /* instance_id */)
 
+// Used by the browser process to forward messages to BrowserPluginObservers.
+IPC_MESSAGE_ROUTED2(BrowserPluginMsg_ForwardMessage,
+                    int /* instance_id */,
+                    IPC::Message /* message */)
+
 // Once the swapped out guest RenderView has been created in the embedder render
 // process, the browser process informs the embedder of its routing ID.
 IPC_MESSAGE_ROUTED2(BrowserPluginMsg_GuestContentWindowReady,