Telemetry support for extensions.

tools/telemetry/telemetry/browser.py

Index: tools/telemetry/telemetry/browser.py
===================================================================
--- tools/telemetry/telemetry/browser.py	(revision 178380)
+++ tools/telemetry/telemetry/browser.py	(working copy)
@@ -4,6 +4,7 @@
 import os
 
 from telemetry import browser_credentials
+from telemetry import extension_list
 from telemetry import tab_list
 from telemetry import temporary_http_server
 from telemetry import wpr_modes
@@ -27,6 +28,10 @@
     self._wpr_server = None
     self._platform = platform
     self._tabs = tab_list.TabList(browser_backend.tab_list_backend)
+    self._extensions = None
+    if not browser_backend.is_content_shell:
+      self._extensions = extension_list.ExtensionList(
+          browser_backend.extension_list_backend)
     self.credentials = browser_credentials.BrowserCredentials()
 
   def __enter__(self):
@@ -57,6 +62,10 @@
     return self._tabs
 
   @property
+  def extensions(self):
+    return self._extensions
+
+  @property
   def supports_tracing(self):
     return self._browser_backend.supports_tracing