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

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1772 matching lines @@
         'arm_float_abi%': '',
         'arm_thumb%': 0,
       }],
 
       # Enable brlapi by default for chromeos.
       [ 'chromeos==1', {
         'use_brlapi%': 1,
       }],
 
       ['use_ozone==1', {
+        # This is the default platform
         'ozone_platform%': "test",
+
+        # Enable built-in ozone platforms if ozone is enabled.
+        'ozone_platform_dri%': 1,
+        'ozone_platform_test%': 1,
       }],
     ],
 
 
     # The path to the ANGLE library. TODO(apatrick): This is to help
     # transition to a new version of ANGLE at a new location. After the
     # transition is complete, this can be removed.
     'angle_path': '<(DEPTH)/third_party/angle_dx11',
 
     # List of default apps to install in new profiles.  The first list contains
@@ skipping 2932 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }