Add testRunner.runIdleTasks() to force idle tasks to run.

content/content_tests.gypi

 # Copyright (c) 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': {
     'layouttest_support_content_sources': [
       'public/test/layouttest_support.h',
       'public/test/nested_message_pump_android.cc',
       'public/test/nested_message_pump_android.h',
@@ skipping 989 matching lines @@
         }],
       ],
     },
     {
       # GN version: //content/test:layouttest_support
       'target_name': 'layouttest_support_content',
       'type': 'static_library',
       'dependencies': [
         'content.gyp:content_renderer',
         'test_support_content',
+        '../components/scheduler/scheduler.gyp:scheduler_test_support',
         '../components/test_runner/test_runner.gyp:test_runner',
         '../skia/skia.gyp:skia',
         '../ui/accessibility/accessibility.gyp:ax_gen',
         '../ui/base/ime/ui_base_ime.gyp:ui_base_ime',
         '../v8/tools/gyp/v8.gyp:v8',
       ],
       'include_dirs': [
         '..',
         '<(SHARED_INTERMEDIATE_DIR)',
       ],
@@ skipping 1193 matching lines @@
                   'content_unittests_apk.isolate',
                 ],
               },
             ],
           },
         ],
       ],
     }],
   ],
 }