Add convenience methods for checking horizontal size class.

This CL adds methods to check for horizontal size class of views, view
controllers, etc.

BUG=527404
R=justincohen@chromium.org,rohitrao@chromium.org

Review URL: https://codereview.chromium.org/1329713002

Cr-Commit-Position: refs/heads/master@{#347211}
(cherry picked from commit ab73901)

TBR=justincohen@chromium.org,rohitrao@chromium.org
NOTRY=true
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1321533006

Cr-Commit-Position: refs/branch-heads/2490@{#160}
Cr-Branched-From: 7790a35-refs/heads/master@{#344925}

ios/chrome/browser/ui/uikit_ui_util.h

@@ -176,10 +176,16 @@ void AddSameCenterYConstraint(UIView* parentView,
                               UIView* subview1,
                               UIView* subview2);
 
+// Whether the |environment| has a compact horizontal size class.
+bool IsCompact(id<UITraitEnvironment> environment);
+
 // Whether the main application window's rootViewController has a compact
 // horizontal size class.
 bool IsCompact();
 
+// Whether the |environment| has a compact iPad horizontal size class.
+bool IsCompactTablet(id<UITraitEnvironment> environment);
+
 // Whether the main application window's rootViewController has a compact
 // iPad horizontal size class.
 bool IsCompactTablet();

ios/chrome/browser/ui/uikit_ui_util.mm

@@ -517,17 +517,25 @@ void AddSameCenterYConstraint(UIView* parentView,
                                           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();
 }