Modified default blacklist regexp to match nothing, as empty regexp

was matching everything. See
http://stackoverflow.com/questions/940822/regular-expression-syntax-for-match-nothing/940856 .

Review URL: http://codereview.chromium.org/601064

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@38965 0039d316-1c4b-4281-b951-d872f2087c98

gcl.py

@@ -1018,7 +1018,7 @@ def Change(change_info, args):
 
 # Valid extensions for files we want to lint.
 DEFAULT_LINT_REGEX = r"(.*\.cpp|.*\.cc|.*\.h)"
-DEFAULT_LINT_IGNORE_REGEX = r""
+DEFAULT_LINT_IGNORE_REGEX = r"$^"
 
 def Lint(change_info, args):
   """Runs cpplint.py on all the files in |change_info|"""