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llvm symbolizer is a more efficient symbolizer than addr2line, objdump,
etc.

In this cl, I 1)created a wrapper instance to interact with
llvm symbolizer, 2)made the stack script to use llvm symbolizer instance,
and then 3)added llvm symbolizer into isolated inputs.

Bug: 774267
Change-Id: I971fb808b97f3a569eb9615f99efa41e3a56f3cb
Reviewed-on: https://chromium-review.googlesource.com/789376Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Zhiling Huang <hzl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521820}