Make CheckLicense() to not trigger on empty files.

presubmit_canned_checks.py

Index: presubmit_canned_checks.py
diff --git a/presubmit_canned_checks.py b/presubmit_canned_checks.py
index 014af28ae2fdd176f4ee27d335417f87939ca5b5..52d93b4fba926ddd95853d4c1e53d3de02722491 100644
--- a/presubmit_canned_checks.py
+++ b/presubmit_canned_checks.py
@@ -275,13 +275,16 @@ def CheckLongLines(input_api, output_api, maxlen=80, source_file_filter=None):
     return []
 
 
-def CheckLicense(input_api, output_api, license, source_file_filter=None):
+def CheckLicense(input_api, output_api, license, source_file_filter=None,
+    accept_empty_files=True):
   """Verifies the license header.
   """
   license_re = input_api.re.compile(license, input_api.re.MULTILINE)
   bad_files = []
   for f in input_api.AffectedSourceFiles(source_file_filter):
     contents = input_api.ReadFile(f, 'rb')
+    if accept_empty_files and not contents:
+      continue
     if not license_re.search(contents):
       bad_files.append(f.LocalPath())
   if bad_files: