Add llvm_url to chromium factory (for libc++ usage)
Add llvm_url to chromium factory (for libc++ usage)

BUG=318770, 313751
R=glider@chromium.org,thakis@chromium.org

See https://codereview.chromium.org/75213003/

Review URL: https://codereview.chromium.org/111723002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@239919 0039d316-1c4b-4281-b951-d872f2087c98

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