Atomic ops cleanup.

Use <stdint.h> instead of "base/basictypes.h".
Put AtomicOps_Internalx86CPUFeaturesInit in the anonymous namespace.
Fix formatting issues.

BUG=

Review URL: https://codereview.chromium.org/143273005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249938 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249938