Upstream Chrome on iOS source code [5/11].

ios/chrome/browser/ui/main/main_view_controller.h

Index: ios/chrome/browser/ui/main/main_view_controller.h
diff --git a/ios/chrome/browser/ui/main/main_view_controller.h b/ios/chrome/browser/ui/main/main_view_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..92ea289597321c9e2f94097bd22fd64a09b649df
--- /dev/null
+++ b/ios/chrome/browser/ui/main/main_view_controller.h
@@ -0,0 +1,18 @@
+// Copyright 2016 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.
+
+#ifndef IOS_CHROME_BROWSER_UI_MAIN_MAIN_VIEW_CONTROLLER_H_
+#define IOS_CHROME_BROWSER_UI_MAIN_MAIN_VIEW_CONTROLLER_H_
+
+#import <UIKit/UIKIt.h>
+
+// A UIViewController that provides a property to maintain a single child view
+// controller.
+@interface MainViewController : UIViewController
+// The child view controller, if any, that is active. Assigning to
+// |activeViewController| will remove any previous active view controller.
+@property(nonatomic, retain) UIViewController* activeViewController;
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_MAIN_MAIN_VIEW_CONTROLLER_H_