GitLab

Add a dialog that can be triggered via LocaleManager that allows a user
to choose their default search engine from a randomized list.

DefaultSearchEnginePromoDialog:
* Add a basic dialog that forces a user to select a default search engine.  This
  dialog only shows up for the "existing user" case and (currently) randomizes
  the search engines available as defined in the TemplateUrlService.

* Add the ability to show the DefaultSearchEnginePromoDialog from the
  LocaleManager.  It currently never fires because the logic hasn't landed, but
  it is triggered from ChromeTabbedActivity and SearchActivity.

Things to do:
- Still trying to figure out how to test this.

Screenshots:
https://drive.google.com/corp/drive/u/0/folders/0B7c8ZkXVwskDRmlnZ1g0LXVpMGM

BUG=714223,712836,712833

Review-Url: https://codereview.chromium.org/2838833002
Cr-Commit-Position: refs/heads/master@{#467766}