Adds labels for Pipelines and ShaderModule. Includes tests. Backend
functionality is implemented for Pipelines, and completed to best effort
for ShaderModule.
Bug: dawn:840
Change-Id: I55024a83f66d9fc2fc0e8b79e4b9a7ebc6f3cf1c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/62860
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Brandon Jones (Intel) <brandon1.jones@intel.com>