This warning was popping up with a new version of the layers when
running the hello_triangle sample. Fix it by assigning the current
Serial ID to the Context for the current pipeline. A more robust
fix in the future would probably be to assign Serial IDs to the
Pipelines themselves.

BUG=angleproject:1898

Change-Id: Ib5e8ea7c4c26907d1987529d8127249f9b18e17f
Reviewed-on: https://chromium-review.googlesource.com/672146Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>