Revert of Disable platform-mode to try and green up tests.

content/content_shell_test_apk_run.isolate

 # Copyright 2015 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.
 {
   'includes': [
     '../build/android/android.isolate',
     'content_shell_test_apk.isolate',
   ],
   'variables': {
     'command': [
       '<(PRODUCT_DIR)/bin/run_content_shell_test_apk',
+      '--enable-platform-mode',
       '-e', 'local', '--apk-under-test',
       '<(PRODUCT_DIR)/apks/ContentShell.apk',
     ],
     'files': [
       '../third_party/proguard/',
       '<(PRODUCT_DIR)/apks/ContentShell.apk',
       '<(PRODUCT_DIR)/apks/ContentShellTest.apk',
       '<(PRODUCT_DIR)/bin/run_content_shell_test_apk',
       '<(PRODUCT_DIR)/test.lib.java/ContentShellTest.jar',
       'content_shell_test_apk.isolate',
     ]
   },
 }