PPAPI: Fix GetBrowserInterface race conditions

ppapi/proxy/plugin_globals.h

Index: ppapi/proxy/plugin_globals.h
diff --git a/ppapi/proxy/plugin_globals.h b/ppapi/proxy/plugin_globals.h
index 5dc614d239bd72f24e84a11b9fd8290f72facdf8..04c333ca93a72393f9d5af70313009d095620e44 100644
--- a/ppapi/proxy/plugin_globals.h
+++ b/ppapi/proxy/plugin_globals.h
@@ -99,10 +99,12 @@ class PPAPI_PROXY_EXPORT PluginGlobals : public PpapiGlobals {
     return &plugin_var_tracker_;
   }
 
-  // The embedder should call set_proxy_delegate during startup.
-  void set_plugin_proxy_delegate(PluginProxyDelegate* d) {
-    plugin_proxy_delegate_ = d;
-  }
+  // The embedder should call SetPluginProxyDelegate during startup.
+  void SetPluginProxyDelegate(PluginProxyDelegate* d);
+  // The embedder may choose to call ResetPluginProxyDelegate during shutdown.
+  // After that point, it's unsafe to call most members of PluginGlobals,
+  // and GetBrowserSender will return NULL.
+  void ResetPluginProxyDelegate();
 
   // Returns the TLS slot that holds the message loop TLS.
   //