Add BoxF::ExpandTo

This will be useful when you need to compute a bounding box for a collection of
3D points.

R=ajuma@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/25518002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226359 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226359