PPAPI: Fix GetBrowserInterface race conditions

ppapi/proxy/plugin_dispatcher.cc

 // 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.
 
 #include "ppapi/proxy/plugin_dispatcher.h"
 
 #include <map>
 
 #include "base/compiler_specific.h"
 #include "base/debug/trace_event.h"
@@ skipping 90 matching lines @@
   return found->second;
 }
 
 // static
 PluginDispatcher* PluginDispatcher::GetForResource(const Resource* resource) {
   return GetForInstance(resource->pp_instance());
 }
 
 // static
 const void* PluginDispatcher::GetBrowserInterface(const char* interface_name) {
-  if (!interface_name) {
-    DLOG(WARNING) << "|interface_name| is null. Did you forget to add "
-        "the |interface_name()| template function to the interface's C++ "
-        "wrapper?";
-    return NULL;
-  }
-
+  // CAUTION: This function is called directly from the plugin, but we *don't*
+  // lock the ProxyLock to avoid excessive locking from C++ wrappers.
   return InterfaceList::GetInstance()->GetInterfaceForPPB(interface_name);
 }
 
 // static
 void PluginDispatcher::LogWithSource(PP_Instance instance,
                                      PP_LogLevel level,
                                      const std::string& source,
                                      const std::string& value) {
   if (!g_live_dispatchers || !g_instance_to_dispatcher)
     return;
@@ skipping 197 matching lines @@
   // once they're set. The user will have to restart to get new font prefs
   // propogated to plugins.
   if (!received_preferences_) {
     received_preferences_ = true;
     preferences_ = prefs;
   }
 }
 
 }  // namespace proxy
 }  // namespace ppapi