[Password Generation] Enable new UI

Replaces key icon and associated bubble with autofill style dropdown. Changes include

- Update PasswordGenerationAgentTest
- Add interactive_uitest for new UI.
- Sync edits to confirmation password field(s).
- Update UMA stats to more accurately reflect user choices. 

Updating the generation popup to match the latest mocks and implement the
editing popup will come in a later CL.

BUG=318977

Review URL: https://codereview.chromium.org/148993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248110 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248110
Add an about flag for enabling the out of process PDF viewer

BUG=303491

Review URL: https://codereview.chromium.org/148963006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248111 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248111