[ios] Fix first run NTP safe area layout.

Bug: 865818
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I4523754e637f1fa9f0cb1c729717e0eeecf334d6
Reviewed-on: https://chromium-review.googlesource.com/1148016Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577552}

ios/chrome/browser/ui/browser_view_controller.mm

@@ -1753,6 +1753,15 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
     [self.primaryToolbarCoordinator.viewController.view setNeedsLayout];
     [self.primaryToolbarCoordinator.viewController.view layoutIfNeeded];
   }
+
+  // Native content pages depend on |self.view|'s safeArea.  If the BVC is
+  // presented underneath another view (such as the first time welcome view),
+  // the BVC has no safe area set during webController's layout initial, and
+  // won't automatically get another layout without forcing it here.
+  Tab* currentTab = [_model currentTab];
+  if ([self isTabNativePage:currentTab]) {
+    [currentTab.webController.view setNeedsLayout];
+  }
 }
 
 - (void)viewDidLayoutSubviews {