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Adds Mojo JavaScript files to web resources. Same JS files are part of
content resources and web mirrors that. This CL is a part of Mojo WebUI
implementation.

Design doc:
https://docs.google.com/document/d/1iUJXX_zoY2BbnecpfxjznOeasf29KUzl_9S_LG08Bes/edit#heading=h.yjqp5garsqf9

BUG=567809

Review-Url: https://codereview.chromium.org/1988863002
Cr-Commit-Position: refs/heads/master@{#394899}