GitLab

To focus geometory calculation, remove the role other than caculation from the
Viewport class.

BUG=245926
TEST=manually

Review URL: https://codereview.chromium.org/382143004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282602 0039d316-1c4b-4281-b951-d872f2087c98