[Telemetry] Fix Chart JSON output typo bug and add unittest

tools/telemetry/telemetry/results/chart_json_output_formatter_unittest.py

Index: tools/telemetry/telemetry/results/chart_json_output_formatter_unittest.py
diff --git a/tools/telemetry/telemetry/results/chart_json_output_formatter_unittest.py b/tools/telemetry/telemetry/results/chart_json_output_formatter_unittest.py
index 6ceacbca0bbb18399d3c985f318d8dc154ed4176..b7359b2cae25685f6c86757000389fd4af3a3c55 100644
--- a/tools/telemetry/telemetry/results/chart_json_output_formatter_unittest.py
+++ b/tools/telemetry/telemetry/results/chart_json_output_formatter_unittest.py
@@ -2,12 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import json
 import os
+import StringIO
 import unittest
-import json
 
 from telemetry import benchmark
 from telemetry.results import chart_json_output_formatter
+from telemetry.results import page_test_results
 from telemetry.page import page_set
 from telemetry.value import scalar
 from telemetry.value import list_of_scalar_values
@@ -21,8 +23,25 @@ def _MakePageSet():
 
 class ChartJsonTest(unittest.TestCase):
   def setUp(self):
+    self._output = StringIO.StringIO()
     self._page_set = _MakePageSet()
     self._benchmark_metadata = benchmark.BenchmarkMetadata('benchmark_name')
+    self._formatter = chart_json_output_formatter.ChartJsonOutputFormatter(
+        self._output, self._benchmark_metadata)
+
+  def testOutputAndParse(self):
+    results = page_test_results.PageTestResults()
+
+    self._output.truncate(0)
+
+    results.WillRunPage(self._page_set[0])
+    v0 = scalar.ScalarValue(results.current_page, 'foo', 'seconds', 3)
+    results.AddValue(v0)
+    results.DidRunPage(self._page_set[0])
+
+    self._formatter.Format(results)
+    d = json.loads(self._output.getvalue())
+    self.assertIn('foo', d['charts'])
 
   def testAsChartDictSerializable(self):
     v0 = scalar.ScalarValue(self._page_set[0], 'foo', 'seconds', 3)