Adding atomic ops for MIPS64.

This change adds atomic operations for MIPS64.

BUG=400684

Review URL: https://codereview.chromium.org/450343002

Cr-Commit-Position: refs/heads/master@{#289624}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289624 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed