Revert of [Mac] Switch from NSObject categories to forward declarations for Touch Bar support.

ui/base/cocoa/touch_bar_forward_declarations.h

 // 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 UI_BASE_COCOA_TOUCH_BAR_FORWARD_DECLARATIONS_H_
 #define UI_BASE_COCOA_TOUCH_BAR_FORWARD_DECLARATIONS_H_
 
-// Once Chrome is built with the 10.12.1 SDK, the NSTouchBar… classes can be
-// referred to normally (instead of with NSClassFromString(@"…")), and this
-// file can be deleted.
+// Once Chrome no longer supports OSX 10.12.0, this file can be deleted.
 
 #import <Foundation/Foundation.h>
 
 #if !defined(MAC_OS_X_VERSION_10_12_1)
-#define __NSi_10_12_1 introduced = 10.12.1
 
-NS_ASSUME_NONNULL_BEGIN
+// The TouchBar classes do not exist at all without the 10.12.1 SDK. When
+// compiling with older SDKs, pretend they are NSObject and add categories to
+// NSObject to expose the methods.
+// To alloc one of these classes, use -[NSClassFromString(@"..") alloc].
 
-@class NSTouchBar, NSTouchBarItem;
-@protocol NSTouchBarDelegate;
+// Incomplete. Add more as necessary.
 
-typedef float NSTouchBarItemPriority;
-static const NSTouchBarItemPriority NSTouchBarItemPriorityHigh = 1000;
-static const NSTouchBarItemPriority NSTouchBarItemPriorityNormal = 0;
-static const NSTouchBarItemPriority NSTouchBarItemPriorityLow = -1000;
+typedef NSObject NSCustomTouchBarItem;
+typedef NSObject NSGroupTouchBarItem;
+typedef NSObject NSTouchBar;
+typedef NSObject NSTouchBarItem;
+typedef NSString* NSTouchBarItemIdentifier;
 
-typedef NSString* NSTouchBarItemIdentifier;
-typedef NSString* NSTouchBarCustomizationIdentifier;
-
-NS_CLASS_AVAILABLE_MAC(10_12_1)
-@interface NSTouchBar : NSObject<NSCoding>
-
-- (instancetype)init NS_DESIGNATED_INITIALIZER;
-- (nullable instancetype)initWithCoder:(NSCoder*)aDecoder
-    NS_DESIGNATED_INITIALIZER;
-
-@property(copy, nullable)
-    NSTouchBarCustomizationIdentifier customizationIdentifier;
-@property(copy) NSArray* customizationAllowedItemIdentifiers;
-@property(copy) NSArray* customizationRequiredItemIdentifiers;
-@property(copy) NSArray* defaultItemIdentifiers;
-@property(copy, readonly) NSArray* itemIdentifiers;
-@property(copy, nullable) NSTouchBarItemIdentifier principalItemIdentifier;
-@property(copy) NSSet* templateItems;
-@property(nullable, weak) id<NSTouchBarDelegate> delegate;
-
-- (nullable __kindof NSTouchBarItem*)itemForIdentifier:
-    (NSTouchBarItemIdentifier)identifier;
-
-@property(readonly, getter=isVisible) BOOL visible;
-
+@protocol NSTouchBarDelegate<NSObject>
 @end
 
-NS_CLASS_AVAILABLE_MAC(10_12_1)
-@interface NSTouchBarItem : NSObject<NSCoding>
-
-- (instancetype)initWithIdentifier:(NSTouchBarItemIdentifier)identifier
-    NS_DESIGNATED_INITIALIZER;
-- (nullable instancetype)initWithCoder:(NSCoder*)coder
-    NS_DESIGNATED_INITIALIZER;
-- (instancetype)init NS_UNAVAILABLE;
-
-@property(readonly, copy) NSTouchBarItemIdentifier identifier;
-@property NSTouchBarItemPriority visibilityPriority;
-@property(readonly, nullable) NSView* view;
-@property(readonly, nullable) NSViewController* viewController;
-@property(readonly, copy) NSString* customizationLabel;
-@property(readonly, getter=isVisible) BOOL visible;
-
+@interface NSObject (FakeNSCustomTouchBarItem)
+@property(readwrite, strong) NSView* view;
 @end
 
-NS_CLASS_AVAILABLE_MAC(10_12_1)
-@interface NSGroupTouchBarItem : NSTouchBarItem
-
+@interface NSObject (FakeNSGroupTouchBarItem)
 + (NSGroupTouchBarItem*)groupItemWithIdentifier:
                             (NSTouchBarItemIdentifier)identifier
                                           items:(NSArray*)items;
-
-@property(strong) NSTouchBar* groupTouchBar;
-@property(readwrite, copy, null_resettable) NSString* customizationLabel;
-
 @end
 
-NS_CLASS_AVAILABLE_MAC(10_12_1)
-@interface NSCustomTouchBarItem : NSTouchBarItem
-
-@property(readwrite, strong) __kindof NSView* view;
-@property(readwrite, strong, nullable)
-    __kindof NSViewController* viewController;
-@property(readwrite, copy, null_resettable) NSString* customizationLabel;
-
+@interface NSObject (FakeNSTouchBar)
+@property(copy) NSArray* defaultItemIdentifiers;
+@property(copy) NSTouchBarItemIdentifier principalItemIdentifier;
+@property(weak) id<NSTouchBarDelegate> delegate;
 @end
 
-@protocol NSTouchBarDelegate<NSObject>
+#elif MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12_1
 
-@optional
-- (nullable NSTouchBarItem*)touchBar:(NSTouchBar*)touchBar
-               makeItemForIdentifier:(NSTouchBarItemIdentifier)identifier
-    NS_AVAILABLE_MAC(10_12_1);
-@end
+// When compiling against the 10.12.1 SDK or later, just provide forward
+// declarations to suppress the partial availability warnings.
 
-NS_ASSUME_NONNULL_END
+@class NSCustomTouchBarItem;
+@class NSGroupTouchBarItem;
+@class NSTouchBar;
+@protocol NSTouchBarDelegate;
+@class NSTouchBarItem;
 
 #endif  // MAC_OS_X_VERSION_10_12_1
 
 #endif  // UI_BASE_COCOA_TOUCH_BAR_FORWARD_DECLARATIONS_H_