[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 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)
 
-// 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].
 
 // Incomplete. Add more as necessary.
 
-typedef NSObject NSCustomTouchBarItem;
-typedef NSObject NSGroupTouchBarItem;
-typedef NSObject NSTouchBar;
-typedef NSObject NSTouchBarItem;
+NS_ASSUME_NONNULL_BEGIN
+
+@protocol NSTouchBarDelegate;
+@class NSTouchBarItem;
+
+typedef float NSTouchBarItemPriority;
+static const NSTouchBarItemPriority NSTouchBarItemPriorityHigh = 1000;
+static const NSTouchBarItemPriority NSTouchBarItemPriorityNormal = 0;
+static const NSTouchBarItemPriority NSTouchBarItemPriorityLow = -1000;
+
 typedef NSString* NSTouchBarItemIdentifier;
+typedef NSString* NSTouchBarCustomizationIdentifier;
 
-@protocol NSTouchBarDelegate<NSObject>
+@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;
+
 @end
 
-@interface NSObject (FakeNSCustomTouchBarItem)
-@property(readwrite, strong) NSView* view;
+@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;
+
 @end
 
-@interface NSObject (FakeNSGroupTouchBarItem)
+@interface NSGroupTouchBarItem : NSTouchBarItem
+
 + (NSGroupTouchBarItem*)groupItemWithIdentifier:
                             (NSTouchBarItemIdentifier)identifier
                                           items:(NSArray*)items;
+
+@property(retain) NSTouchBar* groupTouchBar;
+@property(readwrite, copy, null_resettable) NSString* customizationLabel;
+
 @end
 
-@interface NSObject (FakeNSTouchBar)
-@property(copy) NSArray* defaultItemIdentifiers;
-@property(copy) NSTouchBarItemIdentifier principalItemIdentifier;
-@property(weak) id<NSTouchBarDelegate> delegate;
+@interface NSCustomTouchBarItem : NSTouchBarItem
+
+@property(readwrite, retain) __kindof NSView* view;
+@property(readwrite, retain, nullable)
+    __kindof NSViewController* viewController;
+@property(readwrite, copy, null_resettable) NSString* customizationLabel;
+
 @end
 
+@protocol NSTouchBarDelegate<NSObject>
+@optional
+- (nullable NSTouchBarItem*)touchBar:(NSTouchBar*)touchBar
+               makeItemForIdentifier:(NSTouchBarItemIdentifier)identifier;
+@end
+
+NS_ASSUME_NONNULL_END
+
 #elif MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12_1
 
 // When compiling against the 10.12.1 SDK or later, just provide forward
 // declarations to suppress the partial availability warnings.

[tapted, 2016/11/21 22:32:25]

I think I'm ok with it for now but, if I understand correctly, I think it's
possible we will need to bring these back at some point.

I don't think there's a precedent for putting `*_AVAILABLE_MAC` macros through
our own code. In fact `git grep` doesn't show up any `*_AVAILABLE_MAC` in our
codebase.

It's possible that it makes sense for touchbar stuff -- if we can isolate our
calls to touchbar APIs only within methods that are also declared
NS_AVAILABLE_MAC, then I think that is a good design, and we should proceed with
that approach.

However, it might not always be possible to invoke touchbar APIs only in methods
declared NS_AVAILABLE_MAC -- we might want to just have it between `if
(base::mac::IsAtLeastOS10_Foo())` in a method that can't be declared
NS_AVAILABLE_MAC.

[tapted, 2016/11/23 04:54:22]

Yeah I think removing these broke compilation against the 10.12.1 SDK. Googlers
are probably insulated from it because of the toolchain updates. See
https://echelog.com/logs/browse/chromium/1479855600

 
 @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_