XL layout for message compose

The layout is not final, but it's closer to the wireframe.
- All dimensions and colors are not final.  I just made them up.
- The "+cc/bcc" and "add attachment" buttons are in the wrong position.

I'll wait for the pixel perfect before addressing them.

Bug 3138037

Change-Id: I72fc7557c28e72df08a3751c3c93acfb35749d68
1 file changed