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See design doc in the following link on why we need this page:
https://docs.google.com/document/d/1V9_Xj3MYQ4d_MT30ZpXsdqFoFSJXEvQeMNgXcP5SXjU/edit
All the webui functions are NOTIMPLEMENTED at the moment.
They need some files in https://codereview.chromium.org/2335643002/
before they can be implemented.
To support fast prototyping that requested by UX, this CL
also support override the internal page with remote pages.
So UI can be developed without rebuild Chrome.
That feature is behind enable_vr_shell_ui_dev build flag. We
don't have plan to turn the build flag on.

BUG=
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2341803003
Cr-Commit-Position: refs/heads/master@{#419431}