GitLab

Restructures how NetworkNodes are managed to push more of the code into
the individual implementations of the NetworkGrouper. Grouper is now
more like a factory for a NetworkNode.

In the case here, we are setting up FrameGroupNode as an extension of
NetworkGroupNode which is a lightweight wrapper for groupable items.
When a cell is being rendered we are now able to intercept the calls and
render them with special content (like we do here with product and name
column).

R=pfeldman,dgozman
BUG=718236

Review-Url: https://codereview.chromium.org/2859063003
Cr-Commit-Position: refs/heads/master@{#469583}