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The extract_unwind_tables script dumps the breakpad symbol file and
extracts cfi unwind table from it.
The output format is discussed in this doc:
https://docs.google.com/document/d/1TLuUZ1HaMO6Rv0Q9Y1-w4a-9wcyia1VygQbs4Osb7Oo
This is just a basic format and will be changed in subsequent cl for
size efficiency and performance.

BUG=819888

Change-Id: I987aa2e4ef37f86b6553410d7ee73c15f655495b
Reviewed-on: https://chromium-review.googlesource.com/956971
Commit-Queue: Siddhartha S <ssid@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542736}