Unify various test TaskRunner implementations

Remove various ad-hoc test implementations of TaskRunner and implement TestSimpleTaskRunner instead.

Add TestPendingTask class for use by test TaskRunner implementations.

Clean up TestTaskRunner implementation in net/ and make it use TestPendingTask.

BUG=165806

Review URL: https://codereview.chromium.org/11554036

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@174016 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/single_thread_task_runner.h b/base/single_thread_task_runner.h
index 993d829..a9ba6fd 100644
--- a/base/single_thread_task_runner.h
+++ b/base/single_thread_task_runner.h
@@ -37,4 +37,4 @@
 
 }  // namespace base
 
-#endif  // BASE_SERIAL_TASK_RUNNER_H_
+#endif  // BASE_SINGLE_THREAD_TASK_RUNNER_H_