For some reason, we can't import android.os package in our Constants.

Change-Id: I357ed72d13c5039a83c6e2489cdf5ef74d0ffea8

Note this change does not affect the native decoder interface.

Change-Id: I73b7dc008a5acaf75a31a36a2d332b5afabd82d0

This CL fixes the following compiler warnings.

- Indirect access to static member
- Access to a non-accessible member of an enclosing type
- Parameter assignment
- Method can be static
- Local variable declaration hides another field or variable
- Value of local variable is not used
- Unused import
- Unused private member
- Unnecessary 'else' statement
- Unnecessary declaration of throw exception
- Redundant type arguments
- Missing '@Override' annotation
- Unused '@SuppressWarning' annotations

Bug: 18003991
Change-Id: Icfebe753e53a2cc621848f769d6a3d7ce501ebc7

Bug: 17167221
Bug: 17128331
Change-Id: I6a045fd2398f40dbdc10c9d20993f7513e1f2cff