[ios] Convert BlockedPopupHandler into a tab helper class.

ios/chrome/browser/tabs/tab.mm

Index: ios/chrome/browser/tabs/tab.mm
diff --git a/ios/chrome/browser/tabs/tab.mm b/ios/chrome/browser/tabs/tab.mm
index f1119e3b5c359f7f6e39d7bb94e7a6fbd2aff8ab..3237a500f3476466dc7b9f038a7faf5a93ead662 100644
--- a/ios/chrome/browser/tabs/tab.mm
+++ b/ios/chrome/browser/tabs/tab.mm
@@ -202,8 +202,7 @@ enum class RendererTerminationTabState {
 };
 }  // namespace
 
-@interface Tab ()<BlockedPopupHandlerDelegate,
-                  CRWWebStateObserver,
+@interface Tab ()<CRWWebStateObserver,
                   CRWWebUserInterfaceDelegate,
                   FindInPageControllerDelegate,
                   ReaderModeControllerDelegate> {
@@ -281,9 +280,6 @@ enum class RendererTerminationTabState {
   // Handles autofill.
   base::scoped_nsobject<AutofillController> autofillController_;
 
-  // The popup blocker to show blocked popup to the user.
-  std::unique_ptr<BlockedPopupHandler> popupHandler_;
-
   // Handles find on page.
   base::scoped_nsobject<FindInPageController> findInPageController_;
 
@@ -367,9 +363,6 @@ enum class RendererTerminationTabState {
 // Saves the current title to the history database.
 - (void)saveTitleToHistoryDB;
 
-// Returns a lazily instantiated popup handler.
-- (BlockedPopupHandler*)popupHandler;
-
 // Adds the current session entry to this history database.
 - (void)addCurrentEntryToHistoryDB;
 
@@ -580,6 +573,7 @@ void AddNetworkClientFactoryOnIOThread(
     [self initNativeAppNavigationController];
     // IOSChromeSessionTabHelper comes first because it sets up the tab ID, and
     // other helpers may rely on that.
+    BlockedPopupHandler::CreateForWebState(self.webState);
     IOSChromeSessionTabHelper::CreateForWebState(self.webState);
     NetworkActivityIndicatorTabHelper::CreateForWebState(self.webState,
                                                          self.tabId);
@@ -671,6 +665,9 @@ void AddNetworkClientFactoryOnIOThread(
     // Allow the embedder to attach tab helpers.
     ios::GetChromeBrowserProvider()->AttachTabHelpers(self.webState, self);
 
+    // Allow tab helpers to initialize themselves, if necessary.
+    BlockedPopupHandler::FromWebState(self.webState)->Initialize();
+
     [[NSNotificationCenter defaultCenter]
         addObserver:self
            selector:@selector(applicationDidBecomeActive)
@@ -1661,14 +1658,6 @@ void AddNetworkClientFactoryOnIOThread(
   snapshotOverlayProvider_.reset(snapshotOverlayProvider);
 }
 
-- (BlockedPopupHandler*)popupHandler {
-  if (!popupHandler_.get()) {
-    popupHandler_.reset(new BlockedPopupHandler(self.browserState));
-    popupHandler_->SetDelegate(self);
-  }
-  return popupHandler_.get();
-}
-
 - (void)evaluateU2FResultFromURL:(const GURL&)URL {
   DCHECK(U2FController_);
   [U2FController_ evaluateU2FResultFromU2FURL:URL webState:self.webState];
@@ -2138,7 +2127,8 @@ void AddNetworkClientFactoryOnIOThread(
 
 - (void)webController:(CRWWebController*)webController
         didBlockPopup:(const web::BlockedPopupInfo&)blockedPopupInfo {
-  [self popupHandler]->HandlePopup(blockedPopupInfo);
+  BlockedPopupHandler::FromWebState(self.webState)
+      ->HandlePopup(blockedPopupInfo);
 }
 
 - (CGFloat)headerHeightForWebController:(CRWWebController*)webController {