[GPU] GLES2 lost context recovery

gpu/command_buffer/client/gles2_lib.cc

 // Copyright (c) 2009 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/client/gles2_lib.h"
 #include "gpu/command_buffer/common/thread_local.h"
 
 namespace gles2 {
 namespace {
 gpu::ThreadLocalKey g_gl_context_key;
 }  // namespace anonymous
 
 void Initialize() {
   g_gl_context_key = gpu::ThreadLocalAlloc();
 }
 
 void Terminate() {
   gpu::ThreadLocalFree(g_gl_context_key);
+  g_gl_context_key = 0;
 }
 
 gpu::gles2::GLES2Implementation* GetGLContext() {
   return static_cast<gpu::gles2::GLES2Implementation*>(
     gpu::ThreadLocalGetValue(g_gl_context_key));
 }
 
 void SetGLContext(gpu::gles2::GLES2Implementation* context) {
   gpu::ThreadLocalSetValue(g_gl_context_key, context);
 }
 }  // namespace gles2