AudioRecord: use audio attributes instead of audio source.

Added AudioRecord constructor with audio attributes.
Replaced AudioPolicymanager::getInput() by getInputForAttr().

No new functionality for now.

Also:

- Fixed warnings in AudioPolicyManager
- Allocate audio session ID before calling getOutputForAttr() in
AudioTrack.

Bug: 16006090.
Change-Id: I15df21e4411db688e3096dd801cf579d76d81711