Change from PresubmitError to PresubmitWarning for bad license

We cannot distinguish if this is a moved third-party file. So just
do warnings for a license header from a third-party company.

Bug: 1462922
Change-Id: I78394dcccb9028bce6c535dfce625364dd29157b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4895337
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>

presubmit_canned_checks.py

@@ -805,8 +805,10 @@ def CheckLicense(input_api,
             bad_files.append(f.LocalPath())
     results = []
     if bad_new_files:
+        # We can't distinguish between Google and thirty-party files, so this has to be a
+        # warning rather than an error.
         if license_re_param:
-            error_message = ('License on new files must match:\n\n%s\n' %
+            warning_message = ('License on new files must match:\n\n%s\n' %
                                license_re_param)
         else:
             # Verbatim text that can be copy-pasted into new files (possibly
@@ -819,14 +821,16 @@ def CheckLicense(input_api,
                     'project': project_name,
                     'key_line': key_line,
                 }
-            error_message = (
+            warning_message = (
                 'License on new files must be:\n\n%s\n' % new_license_text +
                 '(adjusting the comment delimiter accordingly).\n\n' +
                 'If this is a moved file, then update the license but do not ' +
-                'update the year.\n\n')
+                'update the year.\n\n' +
-        error_message += 'Found a bad license header in these new or moved files:'
+                'If this is a third-party file then ignore this warning.\n\n')
+        warning_message += 'Found a bad license header in these new or moved files:'
         results.append(
-            output_api.PresubmitError(error_message, items=bad_new_files))
+            output_api.PresubmitPromptWarning(warning_message,
+                                              items=bad_new_files))
     if wrong_year_new_files:
         # We can't distinguish between new and moved files, so this has to be a
         # warning rather than an error.

tests/presubmit_unittest.py

@@ -2555,7 +2555,7 @@ the current line as well!
         self._LicenseCheck(text,
                            license_text,
                            False,
-                           presubmit.OutputApi.PresubmitError,
+                           presubmit.OutputApi.PresubmitPromptWarning,
                            new_file=True)
 
     def _GetLicenseText(self, current_year):