Clean up minor style issues in CacheSideChannel.
Clean up minor style issues in CacheSideChannel.

Copy/move: go/cstyle#Copyable_Movable_Types
Location of the class comment: go/cstyle#Class_Comments

Change-Id: I74a978f3fbfe87ec6c233c4987063e522f8f2578

google/safeside,google/safeside,google/safeside,google/safeside