[Telemetry] Add capability for values to reference external files.

tools/telemetry/telemetry/value/histogram.py

Index: tools/telemetry/telemetry/value/histogram.py
diff --git a/tools/telemetry/telemetry/value/histogram.py b/tools/telemetry/telemetry/value/histogram.py
index f9ebefe11b1d9aed47351734ccc65a0ffe44813c..2da1e943e85eff2266b6f7c42db68215f66ca3a9 100644
--- a/tools/telemetry/telemetry/value/histogram.py
+++ b/tools/telemetry/telemetry/value/histogram.py
@@ -29,9 +29,9 @@ class HistogramValueBucket(object):
 class HistogramValue(value_module.Value):
   def __init__(self, page, name, units,
                raw_value=None, raw_value_json=None, important=True,
-               description=None):
+               description=None, paths=None):
     super(HistogramValue, self).__init__(page, name, units, important,
-                                         description)
+                                         description, paths)
     if raw_value_json:
       assert raw_value == None, \
              'Don\'t specify both raw_value and raw_value_json'
@@ -54,12 +54,13 @@ class HistogramValue(value_module.Value):
     else:
       page_name = None
     return ('HistogramValue(%s, %s, %s, raw_json_string="%s", '
-            'important=%s, description=%s') % (
+            'important=%s, description=%s, paths=%s') % (
               page_name,
               self.name, self.units,
               self.ToJSONString(),
               self.important,
-              self.description)
+              self.description,
+              self.paths)
 
   def GetBuildbotDataType(self, output_context):
     if self._IsImportantGivenOutputIntent(output_context):