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Adds a Snackbar to disclose when an unbound WebAPK or TWA is running in
Chrome. This is designed such that users see the disclosure under the
following conditions:

- The webapp is a TWA or WebAPK
- If it is a WebAPK it was not installed from Chrome.

Until the user presses "OK, got it" the snackbar will persist and
remains during navigation. If a session is ended without pressing
"OK, got it" then the message will appear the next time the app is
opened or resumed.

This appears once per app installation with the caveat that if a user
clears their Chrome data the app will show this message again.

This change is implemented to only start showing the disclosure when
the storage is null. This happens only when an app is opened for the
first time. As such all deployed and launched unbound WebAPKs will not
see this message. To facilitate this we set a boolean flag to show the
message when we launch with null storage. The reason this is necessary
that the default value for a key is false so for existing
unbound WebAPKs we would try to show the message regardless of state
if we didn't use a set, check, clear approach.

Known issues:
It appears that there is a finch trial for chrome modern that isn't
properly initialized if the WebAPK is launched cold (i.e. Chrome
hasn't been started) and Chrome's data has been wiped. As a result,
the old black snackbar is shown instead of the white one. This is
remedied if the app is relaunched and won't occur if Chrome is launched
before the WebAPK.

Bug: 862401
Change-Id: Ieb09b7b628d5718908f8841b06b469c54ed59472
Reviewed-on: https://chromium-review.googlesource.com/1142224
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582187}