Update from https://crrev.com/305340

gpu/command_buffer/build_gles2_cmd_buffer.py

 #!/usr/bin/env python
 # 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.
 
 """code generator for GLES2 command buffers."""
 
 import itertools
 import os
 import os.path
@@ skipping 8291 matching lines @@
     for fname in ['third_party/khronos/GLES2/gl2.h',
                   'third_party/khronos/GLES2/gl2ext.h',
                   'gpu/GLES2/gl2chromium.h',
                   'gpu/GLES2/gl2extchromium.h']:
       lines = open(fname).readlines()
       for line in lines:
         m = enum_re.match(line)
         if m:
           name = m.group(1)
           value = m.group(2)
-          if len(value) <= 10 and not value in dict:
-            dict[value] = name
+          if len(value) <= 10:
+            if not value in dict:
+              dict[value] = name
+            # check our own _CHROMIUM macro conflicts with khronos GL headers.
+            elif dict[value] != name and (name.endswith('_CHROMIUM') or
+                dict[value].endswith('_CHROMIUM')):
+              self.Error("code collision: %s and %s have the same code %s" %
+                         (dict[value], name, value))
 
     file = CHeaderWriter(filename)
     file.Write("static const GLES2Util::EnumToString "
                "enum_to_string_table[] = {\n")
     for value in dict:
       file.Write('  { %s, "%s", },\n' % (value, dict[value]))
     file.Write("""};
 
 const GLES2Util::EnumToString* const GLES2Util::enum_to_string_table_ =
     enum_to_string_table;
@@ skipping 363 matching lines @@
   Format(gen.generated_cpp_filenames)
 
   if gen.errors > 0:
     print "%d errors" % gen.errors
     return 1
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))