Use new tcmalloc on Linux builds by default

Known regressions and test breakages have been fixed.
Changes the default version of tcmalloc used by Chrome on Linux
from a modified tcmalloc 2.0 to a modified tcmalloc 2.7.

BUG=724399,b:70905156

Change-Id: I505b1a3228889fc5eae856e4ad956fc93864609b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1496237
Commit-Queue: Gabriel Marin <gmx@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#653728}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 64d752de1b24b35e27180c1c6e5942294f942544
1 file changed