Update image_decoding to use results.AddValue(...)

tools/perf/measurements/image_decoding.py

 # Copyright 2012 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.
 
 from metrics import power
 from telemetry.page import page_measurement
 from telemetry.timeline import model
+from telemetry.value import scalar
 
 
 class ImageDecoding(page_measurement.PageMeasurement):
   def __init__(self):
     super(ImageDecoding, self).__init__()
     self._power_metric = None
 
   def CustomizeBrowserOptions(self, options):
     options.AppendExtraBrowserArgs('--enable-gpu-benchmarking')
     power.PowerMetric.CustomizeBrowserOptions(options)
@@ skipping 42 matching lines @@
                'image_decoding_measurement_limit_results_to_min_iterations') and
         page.image_decoding_measurement_limit_results_to_min_iterations):
       assert _IsDone()
       min_iterations = tab.EvaluateJavaScript('minIterations')
       decode_image_events = decode_image_events[-min_iterations:]
 
     durations = [d.duration for d in decode_image_events]
     assert durations, 'Failed to find "Decode Image" trace events.'
 
     image_decoding_avg = sum(durations) / len(durations)
-    results.Add('ImageDecoding_avg', 'ms', image_decoding_avg)
-    results.Add('ImageLoading_avg', 'ms',
-                tab.EvaluateJavaScript('averageLoadingTimeMs()'))
+    results.AddValue(scalar.ScalarValue(
+        results.current_page, 'ImageDecoding_avg', 'ms', image_decoding_avg))
+    results.AddValue(scalar.ScalarValue(
+        results.current_page, 'ImageLoading_avg', 'ms',
+        tab.EvaluateJavaScript('averageLoadingTimeMs()')))
 
   def CleanUpAfterPage(self, page, tab):
     if tab.browser.is_tracing_running:
       tab.browser.StopTracing()