Merge "Hold lock when start pending transaction"

        final PendingTransaction pt = mPendingTransactions.remove(0);

        pt.startSync();

        // Post this so that the now-playing transition setup isn't interrupted.

        mService.mH.post(pt::startTransaction);

        mService.mH.post(() -> {

            synchronized (mGlobalLock) {

                pt.startTransaction();

            }

        });

    }

    @Override