PPAPI: Fix GetBrowserInterface race conditions

ppapi/proxy/plugin_globals.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_PROXY_PLUGIN_GLOBALS_H_
 #define PPAPI_PROXY_PLUGIN_GLOBALS_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 81 matching lines @@
       const Preferences& prefs);
 
   // Getters for the plugin-specific versions.
   PluginResourceTracker* plugin_resource_tracker() {
     return &plugin_resource_tracker_;
   }
   PluginVarTracker* plugin_var_tracker() {
     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.
   //
   // If we end up needing more TLS storage for more stuff, we should probably
   // have a struct in here for the different items.
   base::ThreadLocalStorage::Slot* msg_loop_slot() {
     return msg_loop_slot_.get();
   }
 
   // Sets the message loop slot, takes ownership of the given heap-alloated
@@ skipping 71 matching lines @@
   // Member variables should appear before the WeakPtrFactory, see weak_ptr.h.
   base::WeakPtrFactory<PluginGlobals> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginGlobals);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif   // PPAPI_PROXY_PLUGIN_GLOBALS_H_