Allow WebStateObserver to observe N WebStates [28/N].

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

Bug: 775684
Change-Id: I0ab524c26da8afb97753788fa36db0f5df603430
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Reviewed-on: https://chromium-review.googlesource.com/768743
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517062}

ios/chrome/browser/voice/voice_search_navigations_tab_helper.h

@@ -35,6 +35,11 @@ class VoiceSearchNavigationTabHelper
   void NavigationItemCommitted(
       web::WebState* web_state,
       const web::LoadCommittedDetails& load_details) override;
+  void WebStateDestroyed(web::WebState* web_state) override;
+
+  // The WebState this instance is observing. Will be null after
+  // WebStateDestroyed has been called.
+  web::WebState* web_state_ = nullptr;
 
   // Whether a voice search navigation is expected.
   bool will_navigate_to_voice_search_result_ = false;

ios/chrome/browser/voice/voice_search_navigations_tab_helper.mm

@@ -32,8 +32,8 @@ class VoiceSearchNavigationMarker : public base::SupportsUserData::Data {};
 
 VoiceSearchNavigationTabHelper::VoiceSearchNavigationTabHelper(
     web::WebState* web_state)
-    : web::WebStateObserver(web_state) {
-  DCHECK(web_state);
+    : web_state_(web_state) {
+  web_state_->AddObserver(this);
 }
 
 void VoiceSearchNavigationTabHelper::WillLoadVoiceSearchResult() {
@@ -44,7 +44,7 @@ bool VoiceSearchNavigationTabHelper::IsNavigationFromVoiceSearch(
     const web::NavigationItem* item) const {
   DCHECK(item);
   // Check if a voice search navigation is expected if |item| is pending load.
-  const web::NavigationManager* manager = web_state()->GetNavigationManager();
+  const web::NavigationManager* manager = web_state_->GetNavigationManager();
   const web::NavigationItem* pending_item = manager->GetPendingItem();
   const web::NavigationItem* transient_item = manager->GetTransientItem();
   if (item && (item == pending_item || item == transient_item))
@@ -55,11 +55,19 @@ bool VoiceSearchNavigationTabHelper::IsNavigationFromVoiceSearch(
 }
 
 void VoiceSearchNavigationTabHelper::NavigationItemCommitted(
-    web::WebState* web_state_,
+    web::WebState* web_state,
     const web::LoadCommittedDetails& load_details) {
+  DCHECK_EQ(web_state_, web_state);
   if (will_navigate_to_voice_search_result_) {
     load_details.item->SetUserData(
         kNavigationMarkerKey, base::MakeUnique<VoiceSearchNavigationMarker>());
     will_navigate_to_voice_search_result_ = false;
   }
 }
+
+void VoiceSearchNavigationTabHelper::WebStateDestroyed(
+    web::WebState* web_state) {
+  DCHECK_EQ(web_state_, web_state);
+  web_state_->RemoveObserver(this);
+  web_state_ = nullptr;
+}