Linux: remove use_system_mesa bits.

ui/gl/gl.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
 
   'targets': [
@@ skipping 115 matching lines @@
       # hard_dependency is necessary for this target because it has actions
       # that generate header files included by dependent targets. The header
       # files must be generated before the dependents are compiled. The usual
       # semantics are to allow the two targets to build concurrently.
       'hard_dependency': 1,
       'actions': [
         {
           'action_name': 'generate_gl_bindings',
           'variables': {
             'generator_path': 'generate_bindings.py',
-            'conditions': [
-              ['use_system_mesa==0', {
-                'header_paths': '../../third_party/mesa/src/include:../../third_party/khronos',
-              }, { # use_system_mesa==1
-                'header_paths': '/usr/include',
-              }],
-            ],
+            'header_paths': '../../third_party/mesa/src/include:../../third_party/khronos',
           },
           'inputs': [
             '<(generator_path)',
             '<!@(python <(generator_path) --header-paths=<(header_paths) --inputs)',
           ],
           'outputs': [
             '<(gl_binding_output_dir)/gl_bindings_autogen_egl.cc',
             '<(gl_binding_output_dir)/gl_bindings_autogen_egl.h',
             '<(gl_binding_output_dir)/gl_bindings_api_autogen_egl.h',
             '<(gl_binding_output_dir)/gl_bindings_autogen_gl.cc',
@@ skipping 195 matching lines @@
           ],
           'variables': {
             'jni_gen_package': 'ui/gl',
           },
           'includes': [ '../../build/jni_generator.gypi' ],
         },
       ],
     }],
   ],
 }