- Some change on the DrmManager in order to support feature request 4082089.

    In DrmManager, we currently lock both processDrmInfo() and onInfo() which is
    ok for now since processDrmInfo() is async call, and it will return without
    waiting for onInfo() call. However, if we send an event in processDrmInfo(),
    we will got deadlock here because we need to invoke onInf() which will wait
    for processDrmInfo() to release the lock. Use different lock for onInfo().
- Remove some redundent mutex lock.

Change-Id: I59c794f95ba1693425723224114fa975cf9b235f