Remove WebToolbarDelegate from GoogleLandingDataSource.

ios/chrome/browser/ui/ntp/google_landing_mediator.mm

Index: ios/chrome/browser/ui/ntp/google_landing_mediator.mm
diff --git a/ios/chrome/browser/ui/ntp/google_landing_mediator.mm b/ios/chrome/browser/ui/ntp/google_landing_mediator.mm
index 70297c09b0cc80eb88085a480018b9b1c7aba6d3..5dfa2c379cae5256d8907e7b147f4b4517212b6a 100644
--- a/ios/chrome/browser/ui/ntp/google_landing_mediator.mm
+++ b/ios/chrome/browser/ui/ntp/google_landing_mediator.mm
@@ -35,6 +35,7 @@
 #import "ios/chrome/browser/web_state_list/web_state_list_observer_bridge.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ios/public/provider/chrome/browser/voice/voice_search_provider.h"
+#include "ios/web/public/web_state/web_state.h"
 
 using base::UserMetricsAction;
 
@@ -175,6 +176,12 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   [_consumer
       setMaximumMostVisitedSitesShown:[GoogleLandingMediator maxSitesShown]];
   [_consumer setTabCount:self.webStateList->count()];
+  web::WebState* webState = _webStateList->GetActiveWebState();
+  if (webState) {

[rohitrao (ping after 24h), 2017/04/28 10:39:59]

Should we forcibly disable the buttons if there is no webstate?  Do they always
default to the disabled state?  Can we guarantee that?

[justincohen, 2017/04/28 13:23:04]

No, it means this NTP is about to be destroyed.

+    web::NavigationManager* nav = webState->GetNavigationManager();
+    [_consumer setCanGoForward:nav->CanGoForward()];
+    [_consumer setCanGoBack:nav->CanGoBack()];
+  }
 
   // Set up template URL service to listen for default search engine changes.
   _templateURLService =
@@ -278,6 +285,22 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   [self.consumer setTabCount:self.webStateList->count()];
 }
 
+// If the actual webState associated with this mediator were passed in, this
+// would not be necessary.  However, since the active webstate can change when
+// the new tab page is created (and animated in), listen for changes here and
+// always display what's active.
+- (void)webStateList:(WebStateList*)webStateList
+    didChangeActiveWebState:(web::WebState*)newWebState
+                oldWebState:(web::WebState*)oldWebState
+                    atIndex:(int)atIndex
+                 userAction:(BOOL)userAction {
+  if (newWebState) {

[rohitrao (ping after 24h), 2017/04/28 10:39:59]

Same question -- if newWebState is nil, should we disable the buttons?

[justincohen, 2017/04/28 13:23:04]

No, it means this NTP is about to go away.

+    web::NavigationManager* nav = newWebState->GetNavigationManager();
+    [self.consumer setCanGoForward:nav->CanGoForward()];
+    [self.consumer setCanGoBack:nav->CanGoBack()];
+  }
+}
+
 #pragma mark - GoogleLandingDataSource
 
 - (void)addBlacklistedURL:(const GURL&)url {
@@ -317,10 +340,6 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   return IOSChromeLargeIconServiceFactory::GetForBrowserState(_browserState);
 }
 
-- (id<WebToolbarDelegate>)toolbarDelegate {
-  return _webToolbarDelegate;
-}
-
 - (void)promoViewed {
   DCHECK(_notification_promo);
   _notification_promo->HandleViewed();
@@ -350,6 +369,10 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   NOTREACHED();
 }
 
+- (void)prepareToEnterTabSwitcher:(id)sender {

[rohitrao (ping after 24h), 2017/04/28 10:39:59]

Can you document why this call is necessary?

[justincohen, 2017/04/28 13:23:04]

Done.

+  [_webToolbarDelegate prepareToEnterTabSwitcher:sender];

[rohitrao (ping after 24h), 2017/04/28 10:39:59]

I thought you added this method to the DataSource protocol, not to
WebToolbarDelegate?

[justincohen, 2017/04/28 13:23:04]

This is the data source protocol -- note that this goes away in the next
dispatcher CL

+}
+
 #pragma mark - UrlLoader
 
 - (void)loadURL:(const GURL&)url