Wipe out QuotaThreadTask.

This is a one of a series of refactoring patches for QuotaManager.
http://codereview.chromium.org/10872054/
http://codereview.chromium.org/10917060/

BUG=139270

Review URL: https://chromiumcodereview.appspot.com/10919070

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@154987 0039d316-1c4b-4281-b951-d872f2087c98
  void CheckCompleted() {
    if (--waiting_callbacks_ <= 0) {
      DispatchCallbacks();
      DCHECK(callbacks_.empty());

      UsageAndQuotaDispatcherTaskMap& dispatcher_map =
          manager()->usage_and_quota_dispatchers_;
      DCHECK(dispatcher_map.find(host_and_type_) != dispatcher_map.end());
      dispatcher_map.erase(host_and_type_);
      CallCompleted();
    }
  }

  void CheckCompleted() {
    if (--waiting_callbacks_ <= 0) {
      DispatchCallbacks();
      DCHECK(callbacks_.empty());

      UsageAndQuotaDispatcherTaskMap& dispatcher_map =
          manager()->usage_and_quota_dispatchers_;
      DCHECK(dispatcher_map.find(host_and_type_) != dispatcher_map.end());
      dispatcher_map.erase(host_and_type_);
      CallCompleted();
    }
  }
