Support frame tree propagation between renderers in the same browsing instance.

content/common/view_messages.h

Index: content/common/view_messages.h
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index 45b0c4b1cba7dc1ed302de40d064cbcea5abd60c..2e83bcaad02d302c44aebc4c6c2e637233ad9ed5 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -575,6 +575,11 @@ IPC_STRUCT_BEGIN(ViewMsg_PostMessage_Params)
   // equivalent (swapped out) frame in the destination process.  Set to
   // MSG_ROUTING_NONE if the source frame isn't supported (e.g., subframes).

[Charlie Reis, 2012/08/21 01:40:39]

The "e.g., subframes" part is stale now.  Is there ever a case where we'll set
it to MSG_ROUTING_NONE now?

[nasko, 2012/08/21 17:49:42]

It is still technically possible (in code) to return MSG_ROUTING_NONE, since
FromWebView can return NULL. I'm not sure if there is ever a case where
FromWebView will fail. I've removed the last sentence, but I'd like to
understand the behavior here.

   IPC_STRUCT_MEMBER(int, source_routing_id)
+  IPC_STRUCT_MEMBER(int, source_frame_id)
+
+  IPC_STRUCT_MEMBER(int, remote_process_id)

[Charlie Reis, 2012/08/21 01:40:39]

These need a comment explaining why they're here.  It's not immediately obvious
that the renderer should have this information (without our previous
discussion), rather than just sending up the destination frame ID from the
current renderer process and letting the browser translate it.

Also, perhaps rename them to dest_ instead of remote_ (to be consistent with
source_).

[nasko, 2012/08/21 17:49:42]

Actually, I've added the description to the ViewMsg_UpdateFrameTree IPC message,
since the same set of parameters will likely be present in other JS calls being
routed. I've also made it consistent with the post message parameters and called
it target_ instead of remote_.

+  IPC_STRUCT_MEMBER(int, remote_routing_id)
+  IPC_STRUCT_MEMBER(int, remote_frame_id)
 
   // The origin of the source frame.
   IPC_STRUCT_MEMBER(string16, source_origin)
@@ -1038,6 +1043,12 @@ IPC_MESSAGE_ROUTED4(ViewMsg_ScriptEvalRequest,
 IPC_MESSAGE_ROUTED1(ViewMsg_PostMessageEvent,
                     ViewMsg_PostMessage_Params)
 
+// Sends a JSON serialized frame tree to render processes.
+IPC_MESSAGE_ROUTED3(ViewMsg_FrameTree,

[Charlie Reis, 2012/08/21 01:40:39]

Should probably include some kind of verb to make it clear what this is for. 
ViewMsg_UpdateFrameTree?  (This is an instruction from the browser to the
renderer, right?)

[nasko, 2012/08/21 17:49:42]

Done.

+                    int, /* the child process id of the source renderer */

[Charlie Reis, 2012/08/21 01:40:39]

Maybe say "active" instead of "source"?  (I was confusing this with
postMessage's source/dest.)

[nasko, 2012/08/21 17:49:42]

Done.

+                    int, /* route_id of the source renderer */
+                    std::string /* json encoded frame tree */)
+
 // Request for the renderer to evaluate an xpath to a frame and insert css
 // into that frame's document. See ViewMsg_ScriptEvalRequest for details on
 // allowed xpath expressions.
@@ -2192,3 +2203,7 @@ IPC_MESSAGE_ROUTED3(ViewHostMsg_PepperPluginHung,
 // Screen was rotated. Dispatched to the onorientationchange javascript API.
 IPC_MESSAGE_ROUTED1(ViewMsg_OrientationChangeEvent,
                     int /* orientation */)
+
+// Sends a JSON serialized frame tree from the render process to the browser.
+IPC_MESSAGE_ROUTED1(ViewHostMsg_FrameTree,

[Charlie Reis, 2012/08/21 01:40:39]

As above, ViewHostMsg_FrameTreeUpdated.  Also, maybe mention "from the active
renderer process" so that it's clear swapped out RenderViews won't be sending
this.

[nasko, 2012/08/21 17:49:42]

Done.

+                    std::string /* json encoded frame tree */)