Fix some weight bugs in grid layout

This CL also changes how GONE views are considered.
Previously, they would still participate in weight calculations.
Now, they are ignored.

Bug: 19546781

Sub bugs:

Bug: 19571249
Bug: 19571653
Bug: 19571319
Bug: 19571841
Change-Id: I7344f757d3a76be98bb92660f07d2a0cafa9ac12