When there are some changes in the graph, we mark the uses of the reduced
node for revisiting. These are pushed onto a stack and hence follow a
depth first traversal. This sometimes leads to propogating the changes
down the graph and again revisiting the entire graph because of the
nodes that were marked for revisit earlier.

Bug: chromium:725664
Change-Id: I036fd7096c422565a2851b109aba2b4c438403c0
Reviewed-on: https://chromium-review.googlesource.com/563301Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Mythri Alle <mythria@google.com>
Cr-Commit-Position: refs/heads/master@{#46480}