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This adds a class containing the core logic for calling the ItemSuggest
API from chrome. It's owned by the DriveZeroStateProvider, and the logic
can be broken down into three steps:

1. Retrieve oauth2 access tokens for the primary user.
2. Make a request to the ItemSuggest API.
3. Parse the resulting json.

Follow-up CLs will do something with the parsed json, and add unit
tests.

Bug: 1034842
Change-Id: If7b21e9e80d4390615b74a6e4dbebe79a21ced79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2420192Reviewed-by: Rachel Wong <wrong@chromium.org>
Commit-Queue: Tony Yeoman <tby@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809662}