Allow perfmon to benchmark shaders that are defined outside of the repo
Change-Id: Iee53b64cf357facdaa9941602d8d571611680097
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/128040
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>