Add presubmit to check that folks are adding optimized .svg files

Bug: 954683

Change-Id: Id7b8d1da4a69c809de4c2cb943e49c61f77990d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1552569
Commit-Queue: Dan Beam <dbeam@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653629}
8 files changed