Ignore certain messages in plugin broker process if they are not sent by the browser.

content/browser/ppapi_plugin_process_host.h

Index: content/browser/ppapi_plugin_process_host.h
diff --git a/content/browser/ppapi_plugin_process_host.h b/content/browser/ppapi_plugin_process_host.h
index 7c649017633313b0fc7a6cb7667b3753eb38bb8e..46401e8817fec25f35a2ac2e953dfd79c0b468ce 100644
--- a/content/browser/ppapi_plugin_process_host.h
+++ b/content/browser/ppapi_plugin_process_host.h
@@ -36,6 +36,8 @@ class PpapiPluginProcessHost : public BrowserChildProcessHostDelegate,
   class Client {
    public:
     // Gets the information about the renderer that's requesting the channel.
+    // If |renderer_handle| is base::kNullProcessHandle, this channel is used by
+    // the browser itself.
     virtual void GetPpapiChannelInfo(base::ProcessHandle* renderer_handle,
                                      int* renderer_id) = 0;