CallDAG: rewrite assignIndicesInternal as iterative,
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 <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Commit-Queue: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

ppy/angle,ppy/angle,MSOpenTech/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,MSOpenTech/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,ppy/angle,ecoal95/angle,ecoal95/angle