[ios] Fixes an NTP crash when the default search provider is disabled.

ContentSuggestionsCoordinator assumes that TemplateURLService's
GetDefaultSearchProvider() always returns a valid object, which is not
true when the default search engine is disabled (for example, via
policy).

BUG=1148903

Change-Id: I2ba16b900e89c1f3e6c9420b42ea34f9a065f126
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536899Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827416}

ios/chrome/browser/policy/policy_egtest.mm

@@ -172,6 +172,10 @@ void VerifyManagedSettingItem(NSString* accessibilityID,
   [ChromeEarlGrey loadURL:GURL("chrome://policy")];
   [EarlGrey dismissKeyboardWithError:nil];
 
+  // Open a new tab and verify that the NTP does not crash. Regression test for
+  // http://crbug.com/1148903.
+  [ChromeEarlGrey openNewTab];
+
   // Open settings menu.
   [ChromeEarlGreyUI openSettingsMenu];
 

ios/chrome/browser/ui/content_suggestions/content_suggestions_coordinator.mm

@@ -221,9 +221,12 @@
   }
   self.discoverFeedViewController = [self discoverFeed];
 
+  const TemplateURL* defaultURL =
+      templateURLService->GetDefaultSearchProvider();
   BOOL isGoogleDefaultSearchProvider =
-      templateURLService->GetDefaultSearchProvider()->GetEngineType(
-          templateURLService->search_terms_data()) == SEARCH_ENGINE_GOOGLE;
+      defaultURL &&
+      defaultURL->GetEngineType(templateURLService->search_terms_data()) ==
+          SEARCH_ENGINE_GOOGLE;
 
   self.contentSuggestionsMediator = [[ContentSuggestionsMediator alloc]
              initWithContentService:contentSuggestionsService