[ObjC ARC] Converts ios/chrome/browser/ui/stack_view:stack_view to ARC.

ios/chrome/browser/ui/stack_view/stack_view_toolbar_controller.mm

Index: ios/chrome/browser/ui/stack_view/stack_view_toolbar_controller.mm
diff --git a/ios/chrome/browser/ui/stack_view/stack_view_toolbar_controller.mm b/ios/chrome/browser/ui/stack_view/stack_view_toolbar_controller.mm
index cc9fceb3df05bb6dfee78d545ee5aa6d57e74c44..8960e4f9e83fbe35c285b0be674a6b9da0830bd6 100644
--- a/ios/chrome/browser/ui/stack_view/stack_view_toolbar_controller.mm
+++ b/ios/chrome/browser/ui/stack_view/stack_view_toolbar_controller.mm
@@ -12,6 +12,10 @@
 #include "ios/chrome/browser/ui/toolbar/new_tab_button.h"
 #import "ios/chrome/browser/ui/uikit_ui_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 using base::UserMetricsAction;
 
 namespace {
@@ -21,19 +25,19 @@ const CGFloat kBackgroundViewColorAlpha = 0.95;
 }
 
 @implementation StackViewToolbarController {
-  base::scoped_nsobject<UIView> _stackViewToolbar;
-  base::scoped_nsobject<NewTabButton> _openNewTabButton;
+  UIView* _stackViewToolbar;
+  NewTabButton* _openNewTabButton;
 }
 
 - (instancetype)initWithStackViewToolbar {
   self = [super initWithStyle:ToolbarControllerStyleDarkMode];
   if (self) {
-    _stackViewToolbar.reset(
-        [[UIView alloc] initWithFrame:[self specificControlsArea]]);
+    _stackViewToolbar =
+        [[UIView alloc] initWithFrame:[self specificControlsArea]];
     [_stackViewToolbar setAutoresizingMask:UIViewAutoresizingFlexibleHeight |
                                            UIViewAutoresizingFlexibleWidth];
 
-    _openNewTabButton.reset([[NewTabButton alloc] initWithFrame:CGRectZero]);
+    _openNewTabButton = [[NewTabButton alloc] initWithFrame:CGRectZero];
 
     [_openNewTabButton
         setAutoresizingMask:UIViewAutoresizingFlexibleTopMargin |
@@ -61,11 +65,11 @@ const CGFloat kBackgroundViewColorAlpha = 0.95;
 }
 
 - (NewTabButton*)openNewTabButton {
-  return _openNewTabButton.get();
+  return _openNewTabButton;
 }
 
 - (IBAction)recordUserMetrics:(id)sender {
-  if (sender == _openNewTabButton.get())
+  if (sender == _openNewTabButton)
     base::RecordAction(UserMetricsAction("MobileToolbarStackViewNewTab"));
   else
     [super recordUserMetrics:sender];