[Telemetry] Don't create a new Tab object at each navigation.

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

Index: tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py b/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
index 45fc3edd9bf9809c2ce31a4db3a331df1e5101e3..cdc5cb3a69a53dd8d642c53a5fc82608cbfc1559 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/tab_list_backend.py
@@ -1,14 +1,15 @@
 # Copyright 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
 import urllib2
-import weakref
 
-from telemetry.core import util
 from telemetry.core import tab
+from telemetry.core import util
 from telemetry.core.backends.chrome import inspector_backend
 
+
 class TabListBackend(object):
   def __init__(self, browser_backend):
     self._browser_backend = browser_backend
@@ -16,7 +17,7 @@ class TabListBackend(object):
     # Stores web socket debugger URLs in iteration order.
     self._tab_list = []
     # Maps debugger URLs to Tab objects.
-    self._tab_dict = weakref.WeakValueDictionary()
+    self._tab_dict = {}

[dtu, 2014/02/19 23:39:27]

Yay!

Hey, we didn't know about it at the time, but possibly TabListBackend should
extend collections.Sequence and ExtensionDictBackend should extend
collections.Mapping. Just something to think about!

 
   def Init(self):
     self._UpdateTabList()
@@ -68,10 +69,8 @@ class TabListBackend(object):
 
   def GetTabUrl(self, debugger_url):
     tab_info = self._FindTabInfo(debugger_url)
-    # TODO(hartmanng): crbug.com/166886 (uncomment the following assert and
-    # remove the extra None check when _ListTabs is fixed):
-    # assert tab_info is not None
-    return tab_info['url'] if tab_info else None
+    assert tab_info is not None
+    return tab_info['url']
 
   def __iter__(self):
     self._UpdateTabList()