[Telemetry] Add tab API function GetJavascriptStats().

tools/telemetry/telemetry/core/chrome/inspector_memory_unittest.py

Index: tools/telemetry/telemetry/core/chrome/inspector_memory_unittest.py
diff --git a/tools/telemetry/telemetry/core/chrome/inspector_memory_unittest.py b/tools/telemetry/telemetry/core/chrome/inspector_memory_unittest.py
new file mode 100644
index 0000000000000000000000000000000000000000..63d1a6523953a27de4059733c70e23ee49567eca
--- /dev/null
+++ b/tools/telemetry/telemetry/core/chrome/inspector_memory_unittest.py
@@ -0,0 +1,21 @@
+# Copyright (c) 2013 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
+
+from telemetry.test import tab_test_case
+
+class InspectorMemoryTest(tab_test_case.TabTestCase):
+  def testGetDomCounters(self):
+    unittest_data_dir = os.path.join(os.path.dirname(__file__),
+                                     '..', '..', '..', 'unittest_data')
+    self._browser.SetHTTPServerDirectory(unittest_data_dir)
+
+    self._tab.Navigate(
+      self._browser.http_server.UrlOf('dom_counter_sample.html'))
+    self._tab.WaitForDocumentReadyStateToBeComplete()
+
+    counts = self._tab.GetJavascriptStats()
+    self.assertEqual(counts['document_count'], 1)
+    self.assertEqual(counts['node_count'], 14)
+    self.assertEqual(counts['event_listener_count'], 2)