CallDAG: rewrite assignIndicesInternal as iterative, Since the CallDAG is needed to check for the call graph depth, its creation code must be robust to very deep call graphs. BUG=angleproject:1517 Change-Id: I753ab84ad4ced6363a212f0fe94a89aabf4e3c3e Reviewed-on: https://chromium-review.googlesource.com/385496 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>