Expose AppUi from devil utils in browser

telemetry/telemetry/internal/backends/browser_backend.py

Index: telemetry/telemetry/internal/backends/browser_backend.py
diff --git a/telemetry/telemetry/internal/backends/browser_backend.py b/telemetry/telemetry/internal/backends/browser_backend.py
index 43e77733b76e87301009d31dd1f8cdc5d01aac28..3e9f42bd9975706c07a9d0d51b9c5a43900bb694 100644
--- a/telemetry/telemetry/internal/backends/browser_backend.py
+++ b/telemetry/telemetry/internal/backends/browser_backend.py
@@ -95,6 +95,10 @@ class BrowserBackend(app_backend.AppBackend):
     raise NotImplementedError()
 
   @property
+  def supports_app_ui_interactions(self):
+    return False
+
+  @property
   def supports_system_info(self):
     return False