Fix 'make stop' on Mac.
Fix 'make stop' on Mac.

Mac's 'ps' utility has slightly different command line options.
Use a variant that's compatible with both Linux and Mac.

BUG=

Review URL: https://chromiumcodereview.appspot.com/15070007

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@200046 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build