Revert "Revert "Make WatchedFramePop instrumentation event pure-virtual""

Forgot to revert this.

This reverts commit b2c8fc62f4e7889300da2d26294537194e37b926.

Reason for revert: Fixed issue with tests

Change-Id: I1fd5a2759c67a906d55137e2b6548726af2c8e4f
Test: treehugger
4 files changed