rebaseline.py: fix --add-new for JSON files

tools/rebaseline.py

 #!/usr/bin/python
 
 '''
 Copyright 2012 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 '''
 
 '''
@@ skipping 208 matching lines @@
         sections = [gm_json.JSONKEY_ACTUALRESULTS_FAILED]
         if self._add_new:
             sections.append(gm_json.JSONKEY_ACTUALRESULTS_NOCOMPARISON)
         results_to_update = self._GetActualResults(json_url=actuals_url,
                                                    sections=sections)
 
         # Read in current expectations.
         expectations_json_filepath = os.path.join(
             self._expectations_root, subdir, self._expectations_filename)
         expectations_dict = gm_json.LoadFromFile(expectations_json_filepath)
+        expected_results = expectations_dict[gm_json.JSONKEY_EXPECTEDRESULTS]
 
         # Update the expectations in memory, skipping any tests/configs that
         # the caller asked to exclude.
         skipped_images = []
         if results_to_update:
             for (image_name, image_results) in results_to_update.iteritems():
                 (test, config) = \
                     self._image_filename_re.match(image_name).groups()
                 if self._tests:
                     if test not in self._tests:
                         skipped_images.append(image_name)
                         continue
                 if self._configs:
                     if config not in self._configs:
                         skipped_images.append(image_name)
                         continue
-                expectations_dict \
-                    [gm_json.JSONKEY_EXPECTEDRESULTS] \
-                    [image_name] \
+                if not expected_results.get(image_name):
+                    expected_results[image_name] = {}
+                expected_results[image_name] \
                     [gm_json.JSONKEY_EXPECTEDRESULTS_ALLOWEDDIGESTS] = \
                         [image_results]
 
         # Write out updated expectations.
         gm_json.WriteToFile(expectations_dict, expectations_json_filepath)
 
 
 # main...
 
 parser = argparse.ArgumentParser()
@@ skipping 98 matching lines @@
             exception_handler=exception_handler,
             add_new=args.add_new,
             missing_json_is_fatal=missing_json_is_fatal)
 
     try:
         rebaseliner.RebaselineSubdir(subdir=subdir, builder=builder)
     except BaseException as e:
         exception_handler.RaiseExceptionOrContinue(e)
 
 exception_handler.ReportAllFailures()