[Telemetry] Add tab API function GetJavascriptStats().

tools/telemetry/telemetry/core/chrome/inspector_memory.py

Index: tools/telemetry/telemetry/core/chrome/inspector_memory.py
diff --git a/tools/telemetry/telemetry/core/chrome/inspector_memory.py b/tools/telemetry/telemetry/core/chrome/inspector_memory.py
new file mode 100644
index 0000000000000000000000000000000000000000..931cb6e3ead46c0e60a3cf68b5127f379a547d03
--- /dev/null
+++ b/tools/telemetry/telemetry/core/chrome/inspector_memory.py
@@ -0,0 +1,50 @@
+# 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 json
+
+class InspectorMemoryException(Exception):
+  pass
+
+class InspectorMemory(object):
+  """Communicates with the remote inspector's Memory domain."""
+
+  def __init__(self, inspector_backend):
+    self._inspector_backend = inspector_backend
+    self._inspector_backend.RegisterDomain(
+        'Memory',
+        self._OnNotification,
+        self._OnClose)
+
+  def _OnNotification(self, msg):
+    pass
+
+  def _OnClose(self):
+    pass
+
+  def GetDOMCounters(self, timeout):
+    """Retrieves DOM element counts.
+
+    Args:
+      timeout: The number of seconds to wait for the inspector backend to
+          service the request before timing out.
+
+    Returns:
+      A dictionary containing the counts associated with "nodes", "documents",
+      and "jsEventListeners".
+    """
+    res = self._inspector_backend.SyncRequest({
+      'method': 'Memory.getDOMCounters'
+    }, timeout)
+    if ('result' not in res or
+        'nodes' not in res['result'] or
+        'documents' not in res['result'] or
+        'jsEventListeners' not in res['result']):
+      raise InspectorMemoryException(
+          'Inspector returned unexpected result for Memory.getDOMCounters:\n' +
+          json.dumps(res, indent=2))
+    return {
+        'nodes': res['result']['nodes'],
+        'documents': res['result']['documents'],
+        'jsEventListeners': res['result']['jsEventListeners']
+    }