Add means for running some tests only o-o-p, add messaging o-o-p test.

ppapi/proxy/plugin_dispatcher.cc

Index: ppapi/proxy/plugin_dispatcher.cc
diff --git a/ppapi/proxy/plugin_dispatcher.cc b/ppapi/proxy/plugin_dispatcher.cc
index 53dab265f5b6750f38eb402c4979be112cb64c95..f139c7b521f5fa5ce4adc03153cd055923c62566 100644
--- a/ppapi/proxy/plugin_dispatcher.cc
+++ b/ppapi/proxy/plugin_dispatcher.cc
@@ -104,7 +104,6 @@ bool PluginDispatcher::IsPlugin() const {
 }
 
 bool PluginDispatcher::Send(IPC::Message* msg) {
-  DCHECK(MessageLoop::current());

[dmichael (off chromium), 2011/08/16 19:42:26]

Note: I didn't see anything in Send that required being on the main thread.
Clearly there's other work to be done elsewhere, but I think Send needs to be
callable off the main thread.

   TRACE_EVENT2("ppapi proxy", "PluginDispatcher::Send",
                "Class", IPC_MESSAGE_ID_CLASS(msg->type()),
                "Line", IPC_MESSAGE_ID_LINE(msg->type()));