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

content/test/BUILD.gn

 # Copyright 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build_overrides/v8.gni")
@@ skipping 287 matching lines @@
 
   sources =
       rebase_path(content_tests_gypi_values.layouttest_support_content_sources,
                   ".",
                   "//content")
 
   deps = [
     ":test_support",
     "//cc",
     "//cc/blink",
+    "//components/scheduler:test_support",
     "//components/test_runner:test_runner",
     "//content/browser:for_content_tests",
     "//content/public/common",
 
     #"//content/shell:content_shell_lib",
     "//content/renderer:for_content_tests",
     "//mojo/edk/test:test_support",
     "//skia",
     "//ui/accessibility:ax_gen",
     "//v8",
@@ skipping 694 matching lines @@
         "//gpu:test_support",
         "//media/base/android",
         "//media/base/android:media_java",
         "//media/capture/video/android:capture_java",
         "//testing/gmock",
         "//ui/android:ui_java",
       ]
     }
   }
 }