[Android NTP] Move suggestion sections into a separate node.
Also, define how initialization of nodes works, by adding an init()
method that is called after creating a node.
Initialization now happens after the full tree structure has been
created, and recursively processes all nodes in the tree. Subtrees that
are added later use the same pattern; InnerNode now has helper methods
for this.
BUG=
616090
Committed:
https://crrev.com/67606628f1bf101b485ed5fd1ef00fd452e306f7
Cr-Commit-Position: refs/heads/master@{#438135}