[iOS] Stop NTP coordinator when leaving NTP

This CL stops the NTP coordinator when the NTP should be hidden.
This is necessary because crrev.com/c/1953764 remove the call to -stop
in dealloc for the coordinators.

Fixed: 1032191
Change-Id: Ibcd22388b0759ca1ba87cb302dbadb3f3a2277f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1959002Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#723365}

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -4884,7 +4884,10 @@ NSString* const kBrowserViewControllerSnackbarCategory =
     newTabPageCoordinator.webState = webState;
     _ntpCoordinatorsForWebStates[webState] = newTabPageCoordinator;
   } else {
-    DCHECK(_ntpCoordinatorsForWebStates[webState]);
+    NewTabPageCoordinator* newTabPageCoordinator =
+        _ntpCoordinatorsForWebStates[webState];
+    DCHECK(newTabPageCoordinator);
+    [newTabPageCoordinator stop];
     _ntpCoordinatorsForWebStates.erase(webState);
   }
   if (self.active && self.currentWebState == webState) {

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

@@ -199,8 +199,7 @@ GREYElementInteraction* CellWithMatcher(id<GREYMatcher> matcher) {
 // Tests that when tapping a suggestion, it is opened. When going back, the
 // disposition of the collection takes into account the previous scroll, even
 // when more is tapped.
-// TODO(crbug.com/1032191): re-enable when fixed.
-- (void)DISABLED_testOpenPageAndGoBackWithMoreContent {
+- (void)testOpenPageAndGoBackWithMoreContent {
   // Set server up.
   self.testServer->RegisterRequestHandler(base::Bind(&StandardResponse));
   GREYAssertTrue(self.testServer->Start(), @"Test server failed to start.");