Don't DCHECK for non-okay PipelineStatus during ended.

It's possible for a renderer to trigger ended while a demuxer hits an
error which has not yet propagated to WMPI (where Stop() would be
invoked).

BUG=982747
R=sandersd

Change-Id: Ibf225c85ef3d07f342dabf3e60bc835166f4c3da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697435Reviewed-by: Dan Sanders <sandersd@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676606}

media/base/pipeline_impl.cc

@@ -796,7 +796,10 @@ void PipelineImpl::RendererWrapper::CheckPlaybackEnded() {
   if (shared_state_.renderer && !renderer_ended_)
     return;
 
-  DCHECK_EQ(status_, PIPELINE_OK);
+  // Don't fire an ended event if we're already in an error state.
+  if (status_ != PIPELINE_OK)
+    return;
+
   main_task_runner_->PostTask(
       FROM_HERE, base::BindOnce(&PipelineImpl::OnEnded, weak_pipeline_));
 }