TestInterfaces: support delegate clearing.

content/shell/test_runner/test_interfaces.cc

Index: content/shell/test_runner/test_interfaces.cc
diff --git a/content/shell/test_runner/test_interfaces.cc b/content/shell/test_runner/test_interfaces.cc
index deb23193f7356b118e73323deed0bff6b69c51a1..db9fcdba6e14b863b931767506934e591ebd6e6f 100644
--- a/content/shell/test_runner/test_interfaces.cc
+++ b/content/shell/test_runner/test_interfaces.cc
@@ -51,7 +51,10 @@ void TestInterfaces::SetMainView(blink::WebView* web_view) {
 }
 
 void TestInterfaces::SetDelegate(WebTestDelegate* delegate) {
-  gamepad_controller_ = GamepadController::Create(delegate);
+  if (delegate)
+    gamepad_controller_ = GamepadController::Create(delegate);
+  else
+    gamepad_controller_ = nullptr;
   test_runner_->SetDelegate(delegate);
   delegate_ = delegate;
 }