Make it possible to use OSMesa on Android

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 252 matching lines @@
           'sources': [
             'gl_image_egl.cc',
             'gl_image_egl.h',
           ],
           'link_settings': {
             'libraries': [
               '-landroid',
             ],
           },
           'sources!': [
-            'gl_context_osmesa.cc',
             'system_monitor_posix.cc',
           ],
           'defines': [
             'GL_GLEXT_PROTOTYPES',
             'EGL_EGLEXT_PROTOTYPES',
           ],
         }],
         ['OS!="android"', {
           'sources/': [ ['exclude', '^android/'] ],
         }],
@@ skipping 50 matching lines @@
           ],
           'variables': {
             'jni_gen_package': 'ui/gl',
           },
           'includes': [ '../../build/jni_generator.gypi' ],
         },
       ],
     }],
   ],
 }