Add convenience methods for checking horizontal size class.

ios/chrome/browser/ui/uikit_ui_util.mm

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/ui/uikit_ui_util.h"
 
 #import <Accelerate/Accelerate.h>
 #import <Foundation/Foundation.h>
 #import <QuartzCore/QuartzCore.h>
 #import <UIKit/UIKit.h>
@@ skipping 499 matching lines @@
   [parentView addConstraint:[NSLayoutConstraint
                                 constraintWithItem:subview1
                                          attribute:NSLayoutAttributeCenterY
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:subview2
                                          attribute:NSLayoutAttributeCenterY
                                         multiplier:1
                                           constant:0]];
 }
 
-bool IsCompact() {
+bool IsCompact(id<UITraitEnvironment> environment) {
   if (base::ios::IsRunningOnIOS8OrLater()) {
-    UIWindow* keyWindow = [UIApplication sharedApplication].keyWindow;
-    return [keyWindow.traitCollection horizontalSizeClass] ==
+    return environment.traitCollection.horizontalSizeClass ==
            UIUserInterfaceSizeClassCompact;
   } else {
     // Prior to iOS 8, iPad is always regular, iPhone is always compact.
     return !IsIPadIdiom();
   }
 }
 
+bool IsCompact() {
+  UIWindow* keyWindow = [UIApplication sharedApplication].keyWindow;
+  return IsCompact(keyWindow);
+}
+
+bool IsCompactTablet(id<UITraitEnvironment> environment) {
+  return IsIPadIdiom() && IsCompact(environment);
+}
+
 bool IsCompactTablet() {
   return IsIPadIdiom() && IsCompact();
 }