[Mac] Create CrTrackingArea and use it in TabStripController.

chrome/browser/ui/cocoa/tracking_area.mm

+// Copyright (c) 2011 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 "chrome/browser/ui/cocoa/tracking_area.h"
+
+#include "base/logging.h"
+
+// NSTrackingArea does not retain its |owner| so CrTrackingArea wraps the real
+// owner in this proxy, which can stop forwarding messages to the owner when
+// it is no longer |alive_|.
+@interface CrTrackingAreaOwnerProxy : NSObject {
+ @private
+  // Whether or not the owner is "alive" and should forward calls to the real
+  // owner object.
+  BOOL alive_;
+
+  // The real object for which this is a proxy. Weak.
+  id owner_;
+
+  // The Class of |owner_|. When the actual object is no longer alive (and could
+  // be zombie), this allows for introspection.
+  Class ownerClass_;
+}
+@property(nonatomic, assign) BOOL alive;
+- (id)initWithOwner:(id)owner;
+@end
+
+@implementation CrTrackingAreaOwnerProxy
+
+@synthesize alive = alive_;
+
+- (id)initWithOwner:(id)owner {

[Scott Hess - ex-Googler, 2011/02/14 21:13:45]

OK, but now you need if ((self = [super init])) {...}

+  alive_ = YES;
+  owner_ = owner;
+  ownerClass_ = [owner class];
+  return self;
+}
+
+- (void)forwardInvocation:(NSInvocation*)invocation {
+  if (!alive_)
+    return;
+  [invocation invokeWithTarget:owner_];
+}
+
+- (NSMethodSignature*)methodSignatureForSelector:(SEL)sel {
+  // This can be called if |owner_| is not |alive_|, so use the Class to
+  // generate the signature. |-forwardInvocation:| will block the actual call.
+  return [ownerClass_ instanceMethodSignatureForSelector:sel];
+}
+
+- (BOOL)respondsToSelector:(SEL)aSelector {
+  return [ownerClass_ instancesRespondToSelector:aSelector];
+}
+
+@end
+
+// Private Interface ///////////////////////////////////////////////////////////
+
+@interface CrTrackingArea (Private)
+- (void)windowWillClose:(NSNotification*)notif;
+@end
+
+////////////////////////////////////////////////////////////////////////////////
+
+@implementation CrTrackingArea
+
+- (id)initWithRect:(NSRect)rect
+           options:(NSTrackingAreaOptions)options
+             owner:(id)owner
+          userInfo:(NSDictionary*)userInfo {
+  scoped_nsobject<CrTrackingAreaOwnerProxy> ownerProxy(
+      [[CrTrackingAreaOwnerProxy alloc] initWithOwner:owner]);
+  if ((self = static_cast<id>([super initWithRect:rect
+                                          options:options
+                                            owner:ownerProxy.get()
+                                         userInfo:userInfo]))) {
+    ownerProxy_.reset(ownerProxy.release());

[Scott Hess - ex-Googler, 2011/02/14 21:13:45]

Suggest ownerProxy_.swap(ownerProxy);.  I think your existing code is right, but
I definitely find that I have to think about it.  I think that swap() has
identical impact.

+  }
+  return self;
+}
+
+- (void)dealloc {
+  [[NSNotificationCenter defaultCenter] removeObserver:self];
+  [super dealloc];
+}
+
+- (void)clearOwner {
+  [ownerProxy_ setAlive:NO];
+}
+
+- (void)clearOwnerWhenWindowWillClose:(NSWindow*)window {
+  DCHECK(window);
+  NSNotificationCenter* center = [NSNotificationCenter defaultCenter];
+  [center addObserver:self
+             selector:@selector(windowWillClose:)
+                 name:NSWindowWillCloseNotification
+               object:window];
+}
+
+- (void)windowWillClose:(NSNotification*)notif {
+  [self clearOwner];
+}
+
+@end