Implement --ozone-platform flag to select OzonePlatform implementation at runtime

ui/ozone/ozone.gyp

 # Copyright 2013 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,
+    'external_ozone_platforms': [],
     'external_ozone_platform_files': [],
     'external_ozone_platform_deps': [],
   },
   'targets': [
     {
       'target_name': 'ozone',
       'type': '<(component)',
       'dependencies': [
         '<(DEPTH)/base/base.gyp:base',
         '<(DEPTH)/ui/gfx/gfx.gyp:gfx',
         '<(DEPTH)/ui/events/events.gyp:events',
         '<(DEPTH)/skia/skia.gyp:skia',
         '<@(external_ozone_platform_deps)',
       ],
       'defines': [
         'OZONE_IMPLEMENTATION',
       ],
+      'variables': {
+        'platform_list_file': '<(SHARED_INTERMEDIATE_DIR)/ui/ozone/ozone_platform_list.cc',
+        'ozone_platforms': [
+          '<@(external_ozone_platforms)',
+        ],
+      },
       'sources': [
+        '<(platform_list_file)',
         'ozone_platform.cc',
         'ozone_platform.h',
         'ozone_switches.cc',
         'ozone_switches.h',
         'platform/dri/ozone_platform_dri.cc',
         'platform/dri/ozone_platform_dri.h',
         'platform/test/ozone_platform_test.cc',
         'platform/test/ozone_platform_test.h',
         '<@(external_ozone_platform_files)',
       ],
+      'actions': [
+        {
+          'action_name': 'generate_ozone_platform_list',
+          'variables': {
+            'generator_path': 'generate_ozone_platform_list.py',
+          },
+          'inputs': [
+            '<(generator_path)',
+          ],
+          'outputs': [
+            '<(platform_list_file)',
+          ],
+          'action': [
+            'python',
+            '<(generator_path)',
+            '--output_file=<(platform_list_file)',
+            '--default=<(ozone_platform)',
+            '<@(ozone_platforms)',
+          ],
+        },
+      ],
       'conditions': [
-        ['ozone_platform != "dri"', {
+        ['<(ozone_platform_dri)==1', {
+          'variables': {
+            'ozone_platforms': [
+              'dri'
+            ]
+          }
+        }, {  # ozone_platform_dri==0
           'sources/': [
             ['exclude', '^platform/dri/'],
           ]
         }],
-        ['ozone_platform != "test"', {
+        ['<(ozone_platform_test)==1', {
+          'variables': {
+            'ozone_platforms': [
+              'test'
+            ],
+          }
+        }, {  # ozone_platform_test==0
           'sources/': [
             ['exclude', '^platform/test/'],
           ]
         }],
       ]
     },
   ],
 }