[Telemetry] Introduce SummarizableValue.

tools/telemetry/telemetry/web_perf/metrics/gpu_timeline.py

 # Copyright 2015 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.
 import collections
 import math
 import sys
 
 from telemetry.timeline import model as model_module
+from telemetry.value import improvement_direction
 from telemetry.value import list_of_scalar_values
 from telemetry.value import scalar
 from telemetry.web_perf.metrics import timeline_based_metric
 
 TOPLEVEL_GL_CATEGORY = 'gpu_toplevel'
 TOPLEVEL_SERVICE_CATEGORY = 'disabled-by-default-gpu.service'
 TOPLEVEL_DEVICE_CATEGORY = 'disabled-by-default-gpu.device'
 
 SERVICE_FRAME_END_MARKER = (TOPLEVEL_SERVICE_CATEGORY, 'SwapBuffer')
 DEVICE_FRAME_END_MARKER = (TOPLEVEL_DEVICE_CATEGORY, 'SwapBuffer')
 
 TRACKED_GL_CONTEXT_NAME = {'RenderCompositor': 'render_compositor',
                            'BrowserCompositor': 'browser_compositor',
                            'Compositor': 'browser_compositor'}
 
 
 class GPUTimelineListOfValues(list_of_scalar_values.ListOfScalarValues):
   def __init__(self, page, name, values):
-    super(GPUTimelineListOfValues, self).__init__(page, name, 'ms', values)
+    super(GPUTimelineListOfValues, self).__init__(
+        page, name, 'ms', values,
+        improvement_direction=improvement_direction.DOWN)
 
 
 class GPUTimelineValue(scalar.ScalarValue):
   def __init__(self, page, name, value):
-    super(GPUTimelineValue, self).__init__(page, name, 'ms', value)
+    super(GPUTimelineValue, self).__init__(
+      page, name, 'ms', value,
+      improvement_direction=improvement_direction.DOWN)
 
 
 def _CalculateFrameTimes(events_per_frame, event_data_func):
   """Given a list of events per frame and a function to extract event time data,
      returns a list of frame times."""
   times_per_frame = []
   for event_list in events_per_frame:
     event_times = [event_data_func(event) for event in event_list]
     times_per_frame.append(sum(event_times))
   return times_per_frame
@@ skipping 193 matching lines @@
 
     # Add in GPU side traces if it was supported (IE. device traces exist).
     if all_device_events:
       timeline_data[gpu_frame_value] = _GPUFrameTimes(all_device_events)
       for value in TRACKED_GL_CONTEXT_NAME.itervalues():
         gpu_value = (value, 'gpu')
         tracked_gpu_event = tracked_events[gpu_value]
         timeline_data[gpu_value] = _GPUFrameTimes(tracked_gpu_event)
 
     return timeline_data