Unset the Instrumented Callback In Progress Flag Later

Unset the Instrumented Callback In Progress Flag Later

Fixing a race condition in the task manager when two tasks are in flight.

Suppose we have an instrumented task currently running as a result of a callback.
Queue: [A]

Next, [A] makes an async call, returning back. In the meantime [B] gets put on the queue.
Queue: [A] [B]

[A] goes back into execution and finishes. When it finishes, it marks that it's no longer
in an instrumented callback and directly executes [B].

[B] has lost its instrumented callback state during the enqueue into the task queue.
As a result, the task queue throws an error.

The fix here is to unset the instrumented callback state after [B] finishes.

BUG=268429

Review URL: https://chromiumcodereview.appspot.com/22361003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@216139 0039d316-1c4b-4281-b951-d872f2087c98