[Telemetry] Move supports_tab_control to PossibleBrowser.

tools/telemetry/telemetry/core/browser.py

Index: tools/telemetry/telemetry/core/browser.py
diff --git a/tools/telemetry/telemetry/core/browser.py b/tools/telemetry/telemetry/core/browser.py
index b36c565c41e3effe0385fbc0fa86b8175f056955..c317e6a248068e21278e08fa0d926c4ae8925050 100644
--- a/tools/telemetry/telemetry/core/browser.py
+++ b/tools/telemetry/telemetry/core/browser.py
@@ -58,11 +58,6 @@ class Browser(object):
     return self._browser_backend.browser_type
 
   @property
-  def is_content_shell(self):
-    """Returns whether this browser is a content shell, only."""
-    return self._browser_backend.is_content_shell
-
-  @property
   def supports_extensions(self):
     return self._browser_backend.supports_extensions