Looking at traces for #113796, they're a bit harder to read than they should be.

• We do not emit events if we're reusing the last layer tree here: https://github.com/flutter/engine/blob/d0d2aeca8c5cc331e7d2bed69c02655f040afe6b/shell/common/animator.cc#L246.
• We emit an event here https://github.com/flutter/engine/blob/d0d2aeca8c5cc331e7d2bed69c02655f040afe6b/shell/common/animator.cc#L107, but if we reused the layer tree it's not quite right - there was no overhead.
• We emit an event here: https://github.com/flutter/engine/blob/d0d2aeca8c5cc331e7d2bed69c02655f040afe6b/shell/common/animator.cc#L233 is incorrect if we're reusing the last layer tree.

Cleaning this up would help with investigation on that bug and make it a bit clearer about what's happening.