Introduce interface class IProfileAttribute

This patch does not change any functionality but makes it easier to add
unit tests in a later patch.

Bug: 213617178
Test: Compile-tested only.
Change-Id: I6fbbb3297795c9d7ece8fb3263b3a9b0e5115b18
Signed-off-by: Bart Van Assche <bvanassche@google.com>