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Currently it is not easy to test the supersize viewer without uploading
a dev version to the production site. Add option to
upload_html_viewer.py to host locally. Also adds a staging option
because WFH and local development don't mix so well.

Change-Id: Ieb79a47ba836898cf9da28805ce3c6a9a3e208a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485781
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820273}