Add "description" attribute to Value.

tools/telemetry/telemetry/value/string.py

Index: tools/telemetry/telemetry/value/string.py
diff --git a/tools/telemetry/telemetry/value/string.py b/tools/telemetry/telemetry/value/string.py
index 9ca47f5a969e8dc533e989dc446a7b24cf0c4c42..a62832218edb017bf5ca7860707c41ea43233b8f 100644
--- a/tools/telemetry/telemetry/value/string.py
+++ b/tools/telemetry/telemetry/value/string.py
@@ -6,14 +6,15 @@ from telemetry import value as value_module
 from telemetry.value import list_of_string_values
 
 class StringValue(value_module.Value):
-  def __init__(self, page, name, units, value, important=True):
+  def __init__(self, page, name, units, value, important=True,
+               description=None):
     """A single value (float, integer or string) result from a test.
 
     A test that output a hash of the content in a page might produce a
     string value:
        StringValue(page, 'page_hash', 'hash', '74E377FF')
     """
-    super(StringValue, self).__init__(page, name, units, important)
+    super(StringValue, self).__init__(page, name, units, important, description)
     assert isinstance(value, basestring)
     self.value = value
 
@@ -22,11 +23,13 @@ class StringValue(value_module.Value):
       page_name = self.page.url
     else:
       page_name = None
-    return 'ScalarValue(%s, %s, %s, %s, important=%s)' % (
+    return 'StringValue(%s, %s, %s, %s, important=%s, description=%s)' % (
       page_name,
-      self.name, self.units,
+      self.name,
+      self.units,
       self.value,
-      self.important)
+      self.important,
+      self.description)
 
   def GetBuildbotDataType(self, output_context):
     if self._IsImportantGivenOutputIntent(output_context):