Vulkan: Clean up onResourceChanged. Merge this with the internal method to generate a new command graph node. Call onResourceChanged internally in beginWriteResource. Bug: angleproject:2539 Change-Id: Ie33f886c5df7e15ff0b5d690a63fa664b1e964d4 Reviewed-on: https://chromium-review.googlesource.com/1069292 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Luc Ferron <lucferron@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org>