Refactor creation of SadTabView into a tab helper object

ios/web/public/test/fakes/test_web_state.mm

Index: ios/web/public/test/fakes/test_web_state.mm
diff --git a/ios/web/public/test/fakes/test_web_state.mm b/ios/web/public/test/fakes/test_web_state.mm
index 293473e10266e5fd92d5ab5042c32ff1f3f98912..cd4d7226ab40f0fd5fc83cd431ee5329524a51f7 100644
--- a/ios/web/public/test/fakes/test_web_state.mm
+++ b/ios/web/public/test/fakes/test_web_state.mm
@@ -176,6 +176,13 @@ void TestWebState::OnProvisionalNavigationStarted(const GURL& url) {
     observer.ProvisionalNavigationStarted(url);
 }
 
+void TestWebState::OnRenderProcessGone() {
+  for (auto& observer : observers_)
+    observer.RenderProcessGone();
+}
+
+void TestWebState::ShowTransientContentView(CRWContentView* content_view) {}
+
 void TestWebState::SetCurrentURL(const GURL& url) {
   url_ = url;
 }