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

ui/ozone/ozone.gyp

Index: ui/ozone/ozone.gyp
diff --git a/ui/ozone/ozone.gyp b/ui/ozone/ozone.gyp
index 32008b73cf6c7891268f8aae96a20284efe89227..ee5db69d8983d0e462b73d85e77f772ff7a59e3c 100644
--- a/ui/ozone/ozone.gyp
+++ b/ui/ozone/ozone.gyp
@@ -5,6 +5,7 @@
 {
   'variables': {
     'chromium_code': 1,
+    'external_ozone_platforms': [],
     'external_ozone_platform_files': [],
     'external_ozone_platform_deps': [],
   },
@@ -22,7 +23,14 @@
       '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',
@@ -33,13 +41,46 @@
         '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/'],
           ]