Moved the logic of maintaining the current context to gles2 helper library.

third_party/gles2_book/gles2_book.gyp

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'es_util',
       'type': 'static_library',
       'dependencies': [
         '../../gpu/gpu.gyp:gles2_c_lib',
       ],
       'include_dirs': [
         'Common/Include',
       ],
       'all_dependent_settings': {
         'include_dirs': [
           'Common/Include',
         ],
       },
       'sources': [
         'Common/Include/esUtil.h',
-        'Common/Include/esUtil_win.h',
         'Common/Source/esShader.c',
         'Common/Source/esShapes.c',
         'Common/Source/esTransform.c',
         'Common/Source/esUtil.c',
       ],
     },
     {
       'target_name': 'hello_triangle',
       'type': 'static_library',
       'dependencies': [
@@ skipping 71 matching lines @@
       ],
     },
   ]
 }
 
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