Roll abseil_revision 27c30ec671..8f11724067.

Change Log:
https://chromium.googlesource.com/external/github.com/abseil/abseil-cpp/+log/27c30ec671..8f11724067
Full diff:
https://chromium.googlesource.com/external/github.com/abseil/abseil-cpp/+/27c30ec671..8f11724067

Manual change:
Abseil is migrating to ABSL_ prefixed thread annotations, in order to
do so, a backwards compatible absl/base/internal/thread_annotations.h
has been created (with unprefixed thread annotations). This file is
excluded from this CL because unprefixed thread annotations are
problematic to Chromium and they were in fact prefixed by [1] during
every roll.

[1] - https://cs.chromium.org/chromium/src/third_party/abseil-cpp/rename_annotations.sh?l=130-165&rcl=0ec2bec15811f730af0ad00cb3a30b9bc86d821d

Bug: None
Change-Id: Idc60ee93f6354f70e1d24114836d8b4ce8ea9179
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663135
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670106}
38 files changed