Nuke use_acceleration_when_possible

It's now always true, so can be nuked.

BUG=none
TEST=none
R=ben@chromium.org

Review URL: https://codereview.chromium.org/193703002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256196 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256196
base: Add perf tests target and threading perf-test.

Some base utilities are inherently expensive. Part of this
is the underyling operating system cost, but there is also
some overhead in our own code.

Even for operations we can't improve, it's nice to have
visibility into their cost, to guide designs and optimizations.

This patch adds a "base_perftests" target for all platforms,
and adds tests for our tasks posting performance.
base::WaitableEvent, ConditionVariable, and a minimal posix
WaitableEvent are also tested for comparison.

BUG=345471

Review URL: https://codereview.chromium.org/187833004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256197 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256197