[Mac] Avoid "adding unknown subview" warning.

chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm

 // Copyright (c) 2012 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/tabs/tab_strip_controller.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #include <cmath>
 #include <limits>
@@ skipping 126 matching lines @@
 };
 
 CGFloat FlipXInView(NSView* view, CGFloat width, CGFloat x) {
   if (cocoa_l10n_util::ShouldDoExperimentalRTLLayout())
     return [view frame].size.width - x - width;
   return x;
 }
 
 }  // namespace
 
+@interface NSView (PrivateAPI)
+// Called by AppKit to check if dragging this view should move the window.
+// NSButton overrides this method in the same way so dragging window buttons
+// has no effect. NSView implementation returns NSZeroRect so the whole view
+// area can be dragged.
+- (NSRect)_opaqueRectForWindowMoveWhenInTitlebar;
+@end
+
 @interface TabStripController (Private)
 - (void)addSubviewToPermanentList:(NSView*)aView;
 - (void)regenerateSubviewList;
 - (NSInteger)indexForContentsView:(NSView*)view;
 - (NSImage*)iconImageForContents:(content::WebContents*)contents
                          atIndex:(NSInteger)modelIndex;
 - (void)updateIconsForContents:(content::WebContents*)contents
                        atIndex:(NSInteger)modelIndex;
 - (void)layoutTabsWithAnimation:(BOOL)animate
              regenerateSubviews:(BOOL)doUpdate;
@@ skipping 65 matching lines @@
 // http://www.cocoabuilder.com/archive/cocoa/219261-conditional-mousedowncanmovewindow-for-nsview.html
 // http://www.cocoabuilder.com/archive/cocoa/92973-brushed-metal-window-dragging.html
 - (void)trackClickForWindowMove:(NSEvent*)event;
 @end
 
 @implementation TabStripControllerDragBlockingView
 - (BOOL)mouseDownCanMoveWindow {
   return NO;
 }
 
+- (NSRect)_opaqueRectForWindowMoveWhenInTitlebar {
+ return [self bounds];
+}
+
 - (id)initWithFrame:(NSRect)frameRect
          controller:(TabStripController*)controller {
   if ((self = [super initWithFrame:frameRect])) {
     controller_ = controller;
   }
   return self;
 }
 
 // In "rapid tab closure" mode (i.e., the user is clicking close tab buttons in
 // rapid succession), the animations confuse Cocoa's hit testing (which appears
@@ skipping 2081 matching lines @@
   for (int i = 0; i < tabStripModel_->count(); i++) {
     [self updateIconsForContents:tabStripModel_->GetWebContentsAt(i) atIndex:i];
   }
 }
 
 - (void)setVisualEffectsDisabledForFullscreen:(BOOL)fullscreen {
   [tabStripView_ setVisualEffectsDisabledForFullscreen:fullscreen];
 }
 
 @end