Clip Views textfield drag images to selected text.

Paint views::Textfield drag images with views::Labels.
Makes the drag image fit the size of the selected text.
(not as wide as the origin Omnibox/textfield itself)
Use an offset for the image similar to the Unity desktop.

This changes the appearance of split-selection BiDi text.
(doesn't show blank area between the visually split text)
See before/after pictures at http://crbug.com/349105

Remove now unused RenderText::DrawSelectedTextForDrag.

BUG=349105
TEST=Linux Aura and ChromeOS text drag images look good.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/177683005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255310 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255310
Bind before sandbox lockdown on Windows.
Linux is unaffected. All changed code already is inside sandbox.

BUG=348692

Review URL: https://codereview.chromium.org/185293014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255311 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255311