- Update comments for FlashMemory class.
- Split InMemoryFakeFlash to move the fixed-size buffer into the
derived FakeFlashBuffer class.
- Support initializing FakeFlashBuffer to data provided at construction.
- Allow direct access to the underlying fake flash buffer for testing.
- Create utilities for working with byte arrays in byte_utils.h.
Change-Id: I90d33621cb91da079d7213fe7d33823494120e48