Switch CrOS Valgrind bots from 32-bit to 64-bit.
Switch CrOS Valgrind bots from 32-bit to 64-bit.

BUG=124375
TEST=none
Review URL: https://chromiumcodereview.appspot.com/10169015

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@133525 0039d316-1c4b-4281-b951-d872f2087c98

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