veyron/runtimes/google/vsync: add cycle detecting to DAG linking.

When addParent() is used to create a parent/child relationship between
existing nodes, reject the link if it creates a cycle in the DAG.
This is one of the TODO items.

Change-Id: Id3800d2e6e10ed77ec9a952c086af6c1c154bb4c
2 files changed
tree: 0b44a0a49600b942b308ec45af6cd9ff980c2510
  1. examples/
  2. lib/
  3. products/
  4. runtimes/
  5. security/
  6. services/
  7. tools/