Factor out preference-in-storage check to overridable method.

Change-Id: I2fff3192802f8a180330fda66388eda394334a5a
Treat default value that wasn't found as empty value.

Fixes http://code.google.com/p/android/issues/detail?id=33220

Change-Id: If22e8b245f688d922c168aa54c8acf743c0644d7
Core+SystemUI: DA translation

Port from cm-10.1 - minor change from review

Change-Id: I9b98f44cf300d5f72929c78e8aad3c08bee62b21
Merge "Core+SystemUI: DA translation" into cm-10.2
Merge "Factor out preference-in-storage check to overridable method." into cm-10.2
Merge "Treat default value that wasn't found as empty value." into cm-10.2
Merge remote-tracking branch 'cm/cm-10.2' into cm-10.2