Clean up function name mangling code Fix a few incorrect comments about mangled names, and refactor generating mangled names from function call nodes. BUG=angleproject:1490 TEST=angle_unittests Change-Id: I3ee68c4c0982f1a9c28d8e87aafa19f19559bbf8 Reviewed-on: https://chromium-review.googlesource.com/465826 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>