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

tools/telemetry/telemetry/value/__init__.py

Index: tools/telemetry/telemetry/value/__init__.py
diff --git a/tools/telemetry/telemetry/value/__init__.py b/tools/telemetry/telemetry/value/__init__.py
index c4330ecdd92c5da1a3b24217ed9d5e43b2840694..c6e70caa971e69f841414f1ffbb7f2d4bb12d7b6 100644
--- a/tools/telemetry/telemetry/value/__init__.py
+++ b/tools/telemetry/telemetry/value/__init__.py
@@ -42,7 +42,8 @@ SUMMARY_RESULT_OUTPUT_CONTEXT = 'summary-result-output-context'
 class Value(object):
   """An abstract value produced by a telemetry page test.
   """
-  def __init__(self, page, name, units, important, description):
+  def __init__(
+      self, page, name, units, important, description, higher_is_better=None):
     """A generic Value object.
 
     Args:
@@ -56,12 +57,15 @@ class Value(object):
           by default in downstream UIs.
       description: A string explaining in human-understandable terms what this
           value represents.
+      higher_is_better: Whether a higher value is an improvement (True) or a
+          regression (False). None if unknown.

[tonyg, 2014/12/18 17:31:35]

Thinking aloud here... not all Value subclasses have a strict numerical
representation -- for instance FailureValue, StringValue, TraceValue. So that
suggests that higher_is_better doesn't belong in the Value class. There's
probably a variety of solutions, but maybe we're missing a SummarizableValue
class in the hierarchy? The thing to figure out then is whether the stuff in
Summary moves into SummarizableValue or whether it asserts that it only operates
on SummarizableValues (I haven't explored the relationship enough to make a
suggestion).

     """
     self.page = page
     self.name = name
     self.units = units
     self.important = important
     self.description = description
+    self.higher_is_better = higher_is_better
 
   def IsMergableWith(self, that):
     return (self.units == that.units and
@@ -189,6 +193,9 @@ class Value(object):
     if self.page:
       d['page_id'] = self.page.id
 
+    if self.higher_is_better is not None:
+      d['higher_is_better'] = self.higher_is_better
+
     return d
 
   def AsDictWithoutBaseClassEntries(self):
@@ -272,6 +279,9 @@ class Value(object):
 
     d['important'] = False
 
+    if 'higher_is_better' in value_dict:
+      d['higher_is_better'] = value_dict['higher_is_better']
+
     return d
 
 def ValueNameFromTraceAndChartName(trace_name, chart_name=None):