[Telemetry] Add 'important' to JSON output.

tools/telemetry/telemetry/value/value_unittest.py

 # Copyright 2014 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
 import unittest
 
 from telemetry import value
 from telemetry.page import page_set
 
 
@@ skipping 79 matching lines @@
     self.assertFalse(b.IsMergableWith(a))
 
   def testAsDictBaseKeys(self):
     v = ValueForAsDictTest(None, 'x', 'unit', important=True, description=None)
     d = v.AsDict()
 
     self.assertEquals(d, {
           'name': 'x',
           'type': 'baz',
           'units': 'unit',
+          'important': True
         })
 
   def testAsDictWithPage(self):
     page0 = self.pages[0]
 
     v = ValueForAsDictTest(page0, 'x', 'unit', important=False,
                            description=None)
     d = v.AsDict()
 
     self.assertIn('page_id', d)
@@ skipping 80 matching lines @@
           'units': 'unit'
         }
     d1 = {
           'type': 'value_for_from_dict_test',
           'name': 'y',
           'units': 'unit'
         }
     vs = value.Value.ListOfValuesFromListOfDicts([d0, d1], {})
     self.assertEquals(vs[0].name, 'x')
     self.assertEquals(vs[1].name, 'y')