Add ANGLE Platform implementation.

ash/ash_unittests.isolate

 # Copyright (c) 2014 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.
 {
   'conditions': [
     ['use_x11==0', {
       'variables': {
         'command': [
           '../testing/test_env.py',
           '<(PRODUCT_DIR)/ash_unittests<(EXECUTABLE_SUFFIX)',
@@ skipping 46 matching lines @@
     ['OS=="win" and (fastbuild==0 or fastbuild==1)', {
       'variables': {
         'files': [
           '<(PRODUCT_DIR)/ash_unittests.exe.pdb',
         ],
       },
     }],
   ],
   'includes': [
     '../base/base.isolate',
+    '../third_party/angle/angle.isolate',
   ],
 }