Refactor creation of SadTabView into a tab helper object

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

Index: ios/web/public/test/fakes/test_web_state.h
diff --git a/ios/web/public/test/fakes/test_web_state.h b/ios/web/public/test/fakes/test_web_state.h
index ca0a5b47c161634f29a668ddb9373d41fce1f8be..12d9d36d02dcdc339e38f867192ca814c412cb4f 100644
--- a/ios/web/public/test/fakes/test_web_state.h
+++ b/ios/web/public/test/fakes/test_web_state.h
@@ -53,7 +53,7 @@ class TestWebState : public WebState {
   const GURL& GetVisibleURL() const override;
   const GURL& GetLastCommittedURL() const override;
   GURL GetCurrentURL(URLVerificationTrustLevel* trust_level) const override;
-  void ShowTransientContentView(CRWContentView* content_view) override {}
+  void ShowTransientContentView(CRWContentView* content_view) override;
   void AddScriptCommandCallback(const ScriptCommandCallback& callback,
                                 const std::string& command_prefix) override {}
   void RemoveScriptCommandCallback(const std::string& command_prefix) override {
@@ -87,6 +87,7 @@ class TestWebState : public WebState {
   // Notifier for tests.
   void OnPageLoaded(PageLoadCompletionStatus load_completion_status);
   void OnProvisionalNavigationStarted(const GURL& url);
+  void OnRenderProcessGone();
 
  private:
   BrowserState* browser_state_;