Refactor creation of SadTabView into a tab helper object

ios/chrome/browser/tabs/tab.h

Index: ios/chrome/browser/tabs/tab.h
diff --git a/ios/chrome/browser/tabs/tab.h b/ios/chrome/browser/tabs/tab.h
index 7d8fd8adcff9312ea33a4e6502ce39ea33505b11..128f4dbfdcdca873309790cb22e77bc61c369125 100644
--- a/ios/chrome/browser/tabs/tab.h
+++ b/ios/chrome/browser/tabs/tab.h
@@ -11,6 +11,7 @@
 #include <vector>
 
 #import "components/signin/ios/browser/manage_accounts_delegate.h"
+#import "ios/chrome/browser/web/sad_tab_tab_helper_delegate.h"
 #include "ios/net/request_tracker.h"
 #import "ios/web/public/web_state/ui/crw_web_delegate.h"
 #include "ui/base/page_transition_types.h"
@@ -95,7 +96,8 @@ extern NSString* const kProxyPassthroughHeaderValue;
 // desktop Chrome's TabContents in that it encapsulates rendering. Acts as the
 // delegate for the CRWWebController in order to process info about pages having
 // loaded.
-@interface Tab : NSObject<CRWWebDelegate, ManageAccountsDelegate>
+@interface Tab
+    : NSObject<CRWWebDelegate, ManageAccountsDelegate, SadTabTabHelperDelegate>
 
 // Browser state associated with this Tab.
 @property(nonatomic, readonly) ios::ChromeBrowserState* browserState;