gm_json.py: add ability to load JSON file from a string, not just a local file

gm/display_json_results.py

 #!/usr/bin/env python
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Utility to display a summary of JSON-format GM results, and exit with
 a nonzero errorcode if there were non-ignored failures in the GM results.
 
 Usage:
   python display_json_results.py <filename>
@@ skipping 76 matching lines @@
                           do_list=True, do_fail=False),
     gm_json.JSONKEY_ACTUALRESULTS_NOCOMPARISON:
         ResultAccumulator(name='MissingExpectations',
                           do_list=False, do_fail=False),
     gm_json.JSONKEY_ACTUALRESULTS_SUCCEEDED:
         ResultAccumulator(name='Passed',
                           do_list=False, do_fail=False),
   }
 
   success = True
-  json_dict = gm_json.Load(filepath)
+  json_dict = gm_json.LoadFromFile(filepath)
   actual_results = json_dict[gm_json.JSONKEY_ACTUALRESULTS]
   for label, accumulator in results_map.iteritems():
     results = actual_results[label]
     if results:
       for result in results:
         accumulator.AddResult(result)
     print accumulator.GetSummaryLine()
     if accumulator.ShouldSignalFailure():
       success = False
   print '(results marked with [*] will cause nonzero return value)'
   return success
 
 
 if '__main__' == __name__:
   if len(sys.argv) != 2:
     raise Exception('usage: %s <input-json-filepath>' % sys.argv[0])
   sys.exit(0 if Display(sys.argv[1]) else 1)