Fix for b/16400888 - API Review: GridLayout attributes

Column weights specify the relative proportions of space distribution 
within a *row*. With that in mind, I flipped the vertical and horizontal 
axes in the docs - but that was a mistake. This CL flips the docs back. 
The code works the right way around so doesn't need to be modified.

Change-Id: I1a36882eee8d1b9bd7b8ef10e03cbf66de0ac261
(cherry picked from commit 4ae5f5ee917b2014abe3b6e0b99451693cd2b896)