telemetry: Add GetRendererProcessFromTab to timeline model.

tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py

Index: tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
index f8f620bc9d0fabe9d9b466d0b23d8827d656a4b2..169977c8d8eea9791a30d9b01688f243c4405672 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
@@ -252,7 +252,15 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
     """
     if self._tracing_backend is None:
       self._tracing_backend = tracing_backend.TracingBackend(self._port)
-    return self._tracing_backend.StartTracing(custom_categories, timeout)
+    first_nested_call = self._tracing_backend.StartTracing(
+        custom_categories, timeout)
+    for (i, debugger_url) in enumerate(self._browser.tabs):

[nduca, 2013/10/31 07:32:02]

you need to make sure you close the inspector sessions after you enumerate them
so this code needs work.

background: telemetry has a different websocket connection to every tab. By
executing javascript, you open connections even for ones that were previously
not used. So you need to dig into the backend and figure out which ones were
opened just by this iteration and close them down again so we dont purturb the
measurement too much.

This also makes me wonder about whether StartTracing is the right place to do
this, or EndTracing is better. This is gonna be expensive, if you think about
it.

[ernstm, 2013/11/05 00:25:05]

I moved the iteration to StopTracing. Do you think we still need to manually
close the connections there?

+      tab = self.tab_list_backend.Get(i, None)
+      if tab:
+        tab.ExecuteJavaScript('console.time("' + debugger_url + '")')
+        tab.ExecuteJavaScript('console.timeEnd("' + debugger_url + '")')
+        self._tracing_backend.AddTabToMarkerMapping(tab, debugger_url)
+    return first_nested_call
 
   def StopTracing(self):
     """ Stops tracing and returns the result as TraceResult object. """