Enable FrameCapture to dispatch its calls back to Context and replay
them.

Bug: angleproject:3785
Change-Id: I580eff1fca3e39414a9b45bb296e0f3866ea33bc
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1747055
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>