input_api.basename is a function, so printing it out yields:
"The <function basename at 0x7fccd3735410> directory requires..>"

Instead, use it to resolve the local presubmit path that has
requested clang formatting.

R=dpranke@chromium.org
BUG=422332

Review URL: https://codereview.chromium.org/665493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@292491 0039d316-1c4b-4281-b951-d872f2087c98