Allow WebStateObserver to observe N WebStates [18/N].

Convert HistoryTabHelper to directly track registration with
the observed WebState instead of relying on the deprecated
code in WebStateObserver.

Bug: 775684
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I0b3f3b63e599ad2327df155a75549248b8db9b1b
Reviewed-on: https://chromium-review.googlesource.com/766749
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516292}

ios/chrome/browser/history/history_tab_helper.h

@@ -52,10 +52,15 @@ class HistoryTabHelper : public history::Context,
   void DidFinishNavigation(web::WebState* web_state,
                            web::NavigationContext* navigation_context) override;
   void TitleWasSet(web::WebState* web_state) override;
+  void WebStateDestroyed(web::WebState* web_state) override;
 
   // Helper function to return the history service. May return null.
   history::HistoryService* GetHistoryService();
 
+  // The WebState this instance is observing. Will be null after
+  // WebStateDestroyed has been called.
+  web::WebState* web_state_ = nullptr;
+
   // Hold navigation entries that need to be added to the history database.
   // Pre-rendered WebStates do not write navigation data to the history DB
   // immediately, instead they are cached in this vector and added when it

ios/chrome/browser/history/history_tab_helper.mm

@@ -24,7 +24,9 @@
 
 DEFINE_WEB_STATE_USER_DATA_KEY(HistoryTabHelper);
 
-HistoryTabHelper::~HistoryTabHelper() {}
+HistoryTabHelper::~HistoryTabHelper() {
+  DCHECK(!web_state_);
+}
 
 void HistoryTabHelper::UpdateHistoryPageTitle(const web::NavigationItem& item) {
   DCHECK(!delay_notification_);
@@ -60,19 +62,22 @@ void HistoryTabHelper::SetDelayHistoryServiceNotification(
   std::swap(recorded_navigations_, empty_vector);
 
   web::NavigationItem* last_committed_item =
-      web_state()->GetNavigationManager()->GetLastCommittedItem();
+      web_state_->GetNavigationManager()->GetLastCommittedItem();
   if (last_committed_item) {
     UpdateHistoryPageTitle(*last_committed_item);
   }
 }
 
 HistoryTabHelper::HistoryTabHelper(web::WebState* web_state)
-    : web::WebStateObserver(web_state) {}
+    : web_state_(web_state) {
+  web_state_->AddObserver(this);
+}
 
 void HistoryTabHelper::DidFinishNavigation(
     web::WebState* web_state,
     web::NavigationContext* navigation_context) {
-  if (web_state->GetBrowserState()->IsOffTheRecord()) {
+  DCHECK_EQ(web_state_, web_state);
+  if (web_state_->GetBrowserState()->IsOffTheRecord()) {
     return;
   }
 
@@ -87,9 +92,9 @@ void HistoryTabHelper::DidFinishNavigation(
     return;
   }
 
-  DCHECK(web_state->GetNavigationManager()->GetVisibleItem());
+  DCHECK(web_state_->GetNavigationManager()->GetVisibleItem());
   web::NavigationItem* visible_item =
-      web_state->GetNavigationManager()->GetVisibleItem();
+      web_state_->GetNavigationManager()->GetVisibleItem();
   DCHECK(!visible_item->GetTimestamp().is_null());
 
   // Do not update the history database for back/forward navigations.
@@ -152,21 +157,28 @@ void HistoryTabHelper::DidFinishNavigation(
 }
 
 void HistoryTabHelper::TitleWasSet(web::WebState* web_state) {
+  DCHECK_EQ(web_state_, web_state);
   if (delay_notification_) {
     return;
   }
 
   web::NavigationItem* last_committed_item =
-      web_state->GetNavigationManager()->GetLastCommittedItem();
+      web_state_->GetNavigationManager()->GetLastCommittedItem();
 
   if (last_committed_item) {
     UpdateHistoryPageTitle(*last_committed_item);
   }
 }
 
+void HistoryTabHelper::WebStateDestroyed(web::WebState* web_state) {
+  DCHECK_EQ(web_state_, web_state);
+  web_state_->RemoveObserver(this);
+  web_state_ = nullptr;
+}
+
 history::HistoryService* HistoryTabHelper::GetHistoryService() {
   ios::ChromeBrowserState* browser_state =
-      ios::ChromeBrowserState::FromBrowserState(web_state()->GetBrowserState());
+      ios::ChromeBrowserState::FromBrowserState(web_state_->GetBrowserState());
   if (browser_state->IsOffTheRecord())
     return nullptr;