Introduce content::ChildMessageFilter.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index a8ef56df5c119b6854d5fa795326af09ca6636cf..85cb745e17dc5b3d1626b675d48ae719af1118bf 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1326,8 +1326,11 @@ RenderThreadImpl::GetMediaThreadMessageLoopProxy() {
     media_thread_->Start();
 
 #if defined(OS_ANDROID)
+    // XXX should public RenderThread API be changed to replace
+    // Add/RemoveFilter() w/ ChildMessageFilter base class? Would require
+    // updating all existing clients.

[scherkus (not reviewing), 2013/11/07 21:24:23]

jam: this is the real question I have in mind

if you look at browser-side code, I believe you're forced to use
BrowserMessageFilter and the RenderProcessHost API enforces this

in render-side code, the RenderThread API offers
{Add,Remove}Filter(IPC::ChannelProxy::MessageFilter*) ... I haven't finished
auditing all current callers but we might be able to tighten up that API to
enforce using ChildMessageFilter.

WDYT?

     renderer_demuxer_ = new RendererDemuxerAndroid();
-    AddFilter(renderer_demuxer_.get());
+    AddFilter(renderer_demuxer_->get_internal());
 #endif
   }
   return media_thread_->message_loop_proxy();