Vulkan: Fix deleting in-use Pipeline. 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/672146 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>