GitLab

This CL puts the dialog text inside a scroll view so that very long texts don't hide the dialog buttons by making the dialog oversized.
I also removed SetIcon method which isn't used anywhere.

Screenshots:
https://drive.google.com/file/d/0B9q2eN9gDoUIbU9Wb2F0OS1QTjA/edit?usp=sharing (alert)
https://drive.google.com/file/d/0B9q2eN9gDoUIYnh4ZWdFTEJBYVk/edit?usp=sharing (confirm)
https://drive.google.com/file/d/0B9q2eN9gDoUIQlhBS083ZDdGUWM/edit?usp=sharing (prompt)

BUG=391583

Review URL: https://codereview.chromium.org/375873007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282978 0039d316-1c4b-4281-b951-d872f2087c98