Remove unnecessary friend declaration from TaskRunner.

Bug: 112250
Change-Id: I63369b826307acea4b01f15fbc4cbef2f41514a1
Reviewed-on: https://chromium-review.googlesource.com/1137925Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575884}

base/task_runner.h

@@ -136,10 +136,6 @@ class BASE_EXPORT TaskRunner
  protected:
   friend struct TaskRunnerTraits;
 
-  // Only the Windows debug build seems to need this: see
-  // http://crbug.com/112250.
-  friend class RefCountedThreadSafe<TaskRunner, TaskRunnerTraits>;
-
   TaskRunner();
   virtual ~TaskRunner();