Revert "Add a method to atomic add."

This reverts commit eb539cf92f487daf9567ffbbba6b6653406d43ae.

BUG=
TEST=

Review URL: https://codereview.appspot.com/6395051

git-svn-id: http://skia.googlecode.com/svn/trunk@4615 2bbb7eff-a529-9590-31e7-b0007b416f81
7 files changed