Make ShaderTranslatorCache thread safe

gpu/command_buffer/service/shader_translator_cache.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 "gpu/command_buffer/service/shader_translator_cache.h"
 
 namespace gpu {
 namespace gles2 {
 
-ShaderTranslatorCache* ShaderTranslatorCache::GetInstance() {
-  return Singleton<ShaderTranslatorCache>::get();
-}
-
 ShaderTranslatorCache::ShaderTranslatorCache() {
 }
 
 ShaderTranslatorCache::~ShaderTranslatorCache() {
+  DCHECK(cache_.empty());
 }
 
 void ShaderTranslatorCache::OnDestruct(ShaderTranslator* translator) {
   Cache::iterator it = cache_.begin();
   while (it != cache_.end()) {
     if (it->second == translator) {
       cache_.erase(it);
       return;
     }
     it++;
@@ skipping 24 matching lines @@
     cache_[params] = translator;
     translator->AddDestructionObserver(this);
     return translator;
   } else {
     return NULL;
   }
 }
 
 }  // namespace gles2
 }  // namespace gpu