Add a note about false positives on "copyright" word into licenses checker

It is required to scan the entire file for potential copyright references,
as third-party code may appear anywhere in the file, so false positives
are unfortunately inevitable for comments containing the "C-word".

Add a note to the scanner message to provide a hint on that.

BUG=243570
TBR=torne@chromium.org

Review URL: https://codereview.chromium.org/1161943005

Cr-Commit-Position: refs/heads/master@{#333124}

android_webview/tools/copyright_scanner.py

@@ -376,8 +376,11 @@ def ScanAtPresubmit(input_api, output_api):
     results.append(output_api.PresubmitError(
         'The following files contain a third-party license but are not in ' \
         'a listed third-party directory and are not whitelisted. You must ' \
-        'add the following files to the whitelist file ' \
-        '%s:' % _GetWhitelistFileName(input_api),
+        'add the following files to the whitelist file %s\n' \
+        '(Note that if the code you are adding does not actually contain ' \
+        'any third-party code, it may contain the word "copyright", which ' \
+        'should be masked out, e.g. by writing it as "copy-right"):' \
+        '' % _GetWhitelistFileName(input_api),
         sorted(unknown_files)))
   if missing_files:
     results.append(output_api.PresubmitPromptWarning(

android_webview/tools/webview_licenses.py

@@ -97,11 +97,14 @@ def _CheckLicenseHeaders(excluded_dirs_list, whitelisted_files):
   if unknown:
     print 'The following files contain a third-party license but are not in ' \
           'a listed third-party directory and are not whitelisted. You must ' \
-          'add the following files to the whitelist.\n%s' % \
+          'add the following files to the whitelist.\n' \
+          '(Note that if the code you are adding does not actually contain ' \
+          'any third-party code, it may contain the word "copyright", which ' \
+          'should be masked out, e.g. by writing it as "copy-right")\n%s' % \
           '\n'.join(sorted(unknown))
   if missing:
     print 'The following files are whitelisted, but do not exist.\n%s' % \
-        '\n'.join(sorted(missing))
+          '\n'.join(sorted(missing))
   if stale:
     print 'The following files are whitelisted unnecessarily. You must ' \
           'remove the following files from the whitelist.\n%s' % \