Call function when LayerTreeHostImpl generates a LocalSurfaceId

This way client code that needs to know when the LocalSurfaceId changes can
take action.

BUG=922201
TEST=none

Change-Id: I5b19a611f673e766757e51301c0e475e5ed5393c
Reviewed-on: https://chromium-review.googlesource.com/c/1429623
Reviewed-by: Saman Sami <samans@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625324}
20 files changed