Supports cap height in gfx::Font and gfx::FontList.

This CL is a preparation of http://crrev.com/23601006 .

Cap height will be used to determine the fixed baseline of text, especially for Omnibox but not limited to.

Omnibox wants to show Latin characters vertically center, i.e. ABC look just center.  Omnibox also wants to resize the font list so text is small enough to fit in Omnibox.
The baseline is determined from these two restrictions.  All the texts are rendered based on this baseline regardless its height.  Any characters within the height of the font list must fit in Omnibox.

For text controls other than Omnibox, the height of text box may be determined from the height of the font list and the cap height may not be used.
If the height of text box is smaller than the height of the font list, then the text control determines the baseline based on cap height so it shows ABC vertically center.

BUG=146236,264436
TEST=Ran ui_unittests.

Review URL: https://codereview.chromium.org/24240013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226202 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226202
Removed the experimental flag for Chromecast support and the corresponding strings.

BUG=299971

NOTRY=true

Review URL: https://codereview.chromium.org/25266002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226203 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226203