Added support for improvement_direction to relevant values, which is propogated to chartjson.

tools/perf/benchmarks/blink_perf.py

 # Copyright 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.
 
 import os
 
 from telemetry import benchmark
 from telemetry import page as page_module
 from telemetry.core import util
 from telemetry.page import page_set
 from telemetry.page import page_test
+from telemetry.value import improvement_direction
 from telemetry.value import list_of_scalar_values
 
 
 BLINK_PERF_BASE_DIR = os.path.join(util.GetChromiumSrcDir(),
                                    'third_party', 'WebKit', 'PerformanceTests')
 SKIPPED_FILE = os.path.join(BLINK_PERF_BASE_DIR, 'Skipped')
 
 
 def CreatePageSetFromPath(path, skipped_file):
   assert os.path.exists(path)
@@ skipping 216 matching lines @@
 
 # This benchmark is for local testing, doesn't need to run on bots.
 @benchmark.Disabled()
 class BlinkPerfXMLHttpRequest(benchmark.Benchmark):
   tag = 'xml_http_request'
   test = _BlinkPerfMeasurement
 
   def CreatePageSet(self, options):
     path = os.path.join(BLINK_PERF_BASE_DIR, 'XMLHttpRequest')
     return CreatePageSetFromPath(path, SKIPPED_FILE)