PPAPI: Refactor MessageChannel to prep for sync postMessae

content/public/renderer/renderer_ppapi_host.h

Index: content/public/renderer/renderer_ppapi_host.h
diff --git a/content/public/renderer/renderer_ppapi_host.h b/content/public/renderer/renderer_ppapi_host.h
index 4e253e2e2cf3418defd69acfdfb1b26a62752ba1..6c843dc30f93de87cb7f77c99d774a9f1dc5c5d8 100644
--- a/content/public/renderer/renderer_ppapi_host.h
+++ b/content/public/renderer/renderer_ppapi_host.h
@@ -123,6 +123,23 @@ class RendererPpapiHost {
   // Returns true if the plugin is running in process.
   virtual bool IsRunningInProcess() const = 0;
 
+  virtual std::string GetPluginName() const = 0;
+
+  // Used by the embedder to inform this RendererPpapiHost that the associated
+  // plugin module is a host for "external plugins."

[raymes, 2014/05/22 00:25:31]

nit: "external plugins".

[dmichael (off chromium), 2014/05/22 20:18:02]

Technically, the period should be inside the quotes...
http://blog.apastyle.org/apastyle/2011/08/punctuating-around-quotation-marks....

[raymes, 2014/05/22 23:42:33]

Haha ok, I guess I'm used to the "British style" :) Sorry for the noise.

+  //
+  // An embedder may, at the time a plugin module is created, configure it to
+  // be a host for external plugins. Instances of such plugins go through two
+  // two stages of initialization; the first stage initializes a host plugin
+  // instance, which then loads and initializes a child plugin which takes
+  // over control. These are treated as one Pepper Instance, because despite the
+  // two-stage initialization process, the host and child appear to blink as
+  // one plugin instance.
+  //
+  // The host plugin appears as an in-process plugin, while we interact with the
+  // child plugin via the Pepper proxy.
+  virtual void SetToExternalPluginHost() = 0;

[raymes, 2014/05/22 00:25:31]

Can we do this without modifying the content API? It seems like we know when we
create an "external" module:
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/p...

I think we could store that in the plugin module and then just return it.

[dmichael (off chromium), 2014/05/22 20:18:02]

Unfortunately, that wouldn't work. That function basically clones a Module to
make a new one, and this happens at the point that the instance switches from
the external plugin "host" (really, the trusted NaCl plugin) to the actual
external plugin (the untrusted NaCl app):
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/p...
What I need to know is if the instance we're Initialize()ing is a host of
external plugins (i.e., the NaCl trusted plugin), so the module it looks at is
the one associated with that in-process trusted NaCl plugin.

It's admittedly gross and confusing in the short term (mostly because of the
trusted plugin which switches control to an untrusted plugin). But I think we're
ultimately going to want other hooks for NaCl, even when we get rid of the
trusted plugin.

[raymes, 2014/05/22 23:42:33]

I see, thanks for the explanation.

+
   // There are times when the renderer needs to create a ResourceHost in the
   // browser. This function does so asynchronously. |nested_msgs| is a list of
   // resource host creation messages and |instance| is the PP_Instance which