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- Add a prefix replacement for chrome://resources, since this is needed
across various Web UI pages
- Always add Polymer 3 arguments to closure_flags, even if they are
defined by the invoker. This allows Polymer 3 pages to set additional
prefixes without having to also re-add the polymer 3 closure arguments.

Bug: 965770
Change-Id: Id377a4c454862794ef4330e148615d987bc19030
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1742445Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685246}