PackageManager: Fix concurrent access to shared state

Stop multiple threads from all calling add on the same HashMap.

Cleanup the use of a boolean flag by removing concurrent writes
to it.

Change-Id: I8d61fe7294dcb67ee7d0d7de88d90d2051c310e6
Fix Javadoc link for getModifierBehavior()

Change-Id: I571db5147a081fcd7190483ba9e7a45b46db224d
Add android_system_label to symbols.xml

Change-Id: Id5ae4f440becb5039b189ea59a5c459178550e46
resume: fix recents showing up when waking the device with the home button

Screen is on but dispatcher is not enabled yet.

Change-Id: Ib98d595563ed3df5c7a1e6e4d5a4da83a721537c