[RunLoop] Do not check |sequence_checker_| from ~RunLoop()

It is safe not to if ~RunLoop happens-after Quit() (or if the loop never
ran). Off-thread destruction happens sometimes in RefCountedThreadSafe
objects after the loop was quit (see failures on patch set 1).

Bug: 715235
Change-Id: If3d6e3661d9bc00547ac5606075b3fe066ff3e7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1671868
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683386}

base/run_loop.cc

@@ -124,8 +124,11 @@ RunLoop::RunLoop(Type type)
 }
 
 RunLoop::~RunLoop() {
-  // TODO(gab): Fix bad usage and enable this check, http://crbug.com/715235.
-  // DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  // ~RunLoop() must happen-after the RunLoop is done running but it doesn't
+  // have to be on |sequence_checker_| (it usually is but sometimes it can be a
+  // member of a RefCountedThreadSafe object and be destroyed on another thread
+  // after being quit).
+  DCHECK(!running_);
 }
 
 void RunLoop::Run() {