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This CL enables extraction of unwind tables for chrome when
is_official_build is set to true and when android_channel is not set to
a release channel. This affects build time only on official builds.
Also, Set legacy heap profiler to use unwinder for profiling.

TBR=dpranke@chromium.org
BUG=819888

Change-Id: If9732b5ac1f9dff49c58e88e2ffb6cb387715244
Reviewed-on: https://chromium-review.googlesource.com/976944Reviewed-by: Siddhartha S <ssid@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: Siddhartha S <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546425}