Bug: 152453213
Tag: #refactor
This commit prepares PropertyInvalidatedCache to function as a system
api. The changes may be summarized as follows:
1. Visibility changes - some formerly protected or public methods are
now private.
2. Use of ParcelFileDescriptor instead of FileDescriptor.
3. Null-ness annotations have been added to public methods.
4. An onTrimMemory() method has been created that hides some class
internals from ActivityThread.
An existing test (os/PropertyInvalidatedCacheTest) has been deleted.
Its contents have been merged into app/PropertyInvalidatedCacheTests.
The deleted test may never have been used.
Test: atest PropertyInvalidatedCacheTests
Change-Id: I619e715c3deca016b21c69bf34a8e61771957e68
80f4322b36