Enable crash keys for the browser IO thread

This will help us track down where crashing tasks come from.

Bug: 1024587
Change-Id: I084e915026d9df963b5f4ddae551e7d070ce4449
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917209
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Commit-Queue: Tobias Sargeant <tobiasjs@chromium.org>
Auto-Submit: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Tobias Sargeant <tobiasjs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716106}

content/browser/scheduler/browser_io_thread_delegate.cc

@@ -105,6 +105,7 @@ void BrowserIOThreadDelegate::BindToCurrentThread(
       base::MessagePump::Create(base::MessagePumpType::IO));
   sequence_manager_->SetTimerSlack(timer_slack);
   sequence_manager_->SetDefaultTaskRunner(GetDefaultTaskRunner());
+  sequence_manager_->EnableCrashKeys("io_scheduler_async_stack");
 
   if (task_executor_) {
     base::SetTaskExecutorForCurrentThread(task_executor_);