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This patches the python zipfile implementation to ignore struct unpack errors
in _decodeExtra. See http://bugs.python.org/issue14315

Also adds a --verbose option that enables a bunch of logging to help diagnose
failed symbolization.

Fixes stack tool for gn builds where libs are put in the top-level output
directory.

Review URL: https://codereview.chromium.org/1006603002

Cr-Commit-Position: refs/heads/master@{#325573}