[Telemetry] Add tab API function GetJavascriptStats().

tools/telemetry/telemetry/core/tab.py

Index: tools/telemetry/telemetry/core/tab.py
diff --git a/tools/telemetry/telemetry/core/tab.py b/tools/telemetry/telemetry/core/tab.py
index 6e5c804892f7179365e67081daf4677f90401c39..29f35400dab37ee3159bb47ab5c711bf2a82600f 100644
--- a/tools/telemetry/telemetry/core/tab.py
+++ b/tools/telemetry/telemetry/core/tab.py
@@ -70,3 +70,20 @@ class Tab(web_contents.WebContents):
   def GetCookieByName(self, name, timeout=DEFAULT_TAB_TIMEOUT):
     """Returns the value of the cookie by the given |name|."""
     return self._inspector_backend.GetCookieByName(name, timeout)
+
+  def GetJavascriptStats(self, timeout=DEFAULT_TAB_TIMEOUT):

[nduca, 2013/03/13 03:58:44]

GetDOMStats?

Sorry if you suggested that in the past and I hated it! :$ I'm fine with your
discretion at this point, this looks really good

[dennis_jeffrey, 2013/03/13 21:42:46]

Yes, GetDOMStats sounds good to me.  I made that change.

+    """Returns a dictionary populated with measured Javascript statistics.
+
+    Currently this function returns:
+    {
+      'document_count': integer,
+      'node_count': integer,
+      'event_listener_count': integer
+    }
+    """
+    dom_counters = self._inspector_backend.GetDomCounters(timeout)

[nduca, 2013/03/13 03:58:44]

DOM or Dom? Just curious tbh.

Shoudl the name match the backend name? E.g. GetDomStats? That it turns into an
inspector-level GetDomCounters can just be sealed inside the backend.

[dennis_jeffrey, 2013/03/13 21:42:46]

Actually I prefer DOM when typing in MixedCase, so made that change.

I knew somebody who always wanted acronyms in MixedCaseFunctionNames to have
only the very first letter capitalized, so sometimes I do that without thinking.
 However, I couldn't find a chromium Python style rule talking about this
particular point, so I think it's just best to be consistent.
Done.

+    return {
+      'document_count': dom_counters['documents'],

[nduca, 2013/03/13 03:58:44]

Should this conversion to the expected return type done inside the inspector
backend? Then this is just return the backend properties and maybe an assertion
that the expected values [and only the expected values] are in the return value.

[dennis_jeffrey, 2013/03/13 21:42:46]

Done.

+      'node_count': dom_counters['nodes'],
+      'event_listener_count': dom_counters['jsEventListeners']
+    }