Currently the output is:

Found line ending with white spaces in:
cc/trees/layer_tree_host_impl_unittest.cc, line 379

This format is extremely annoying because you must combine the
file and line number together by hand. A more standard format
for expressing a position in a file is filename:lineno. This
changes the format to match:

Found line ending with white spaces in:
cc/trees/layer_tree_host_impl_unittest.cc:379

R=maruel@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/22837004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@217405 0039d316-1c4b-4281-b951-d872f2087c98