[Telemetry] Clean separation between tab (public API) and tab_backend (Chrome implementation). Flat…

tools/telemetry/telemetry/browser_backend.py

Index: tools/telemetry/telemetry/browser_backend.py
diff --git a/tools/telemetry/telemetry/browser_backend.py b/tools/telemetry/telemetry/browser_backend.py
index 153c4d13dc14bc2b937c79f7150ec27762b786c6..643231d1839d6acea3db747c044642ef968bc54d 100644
--- a/tools/telemetry/telemetry/browser_backend.py
+++ b/tools/telemetry/telemetry/browser_backend.py
@@ -13,6 +13,7 @@ import weakref
 from telemetry import browser_gone_exception
 from telemetry import options_for_unittests
 from telemetry import tab
+from telemetry import tab_backend
 from telemetry import tracing_backend
 from telemetry import user_agent
 from telemetry import util
@@ -96,7 +97,9 @@ class TabController(object):
     # Lazily get/create a Tab object.
     tab_object = self._tab_dict.get(debugger_url)
     if not tab_object:
-      tab_object = tab.Tab(self._browser, self._browser_backend, debugger_url)
+      backend = tab_backend.TabBackend(
+          self._browser, self._browser_backend, debugger_url)
+      tab_object = tab.Tab(backend)
       self._tab_dict[debugger_url] = tab_object
     return tab_object