[Mac] Avoid "adding unknown subview" warning.

chrome/browser/ui/cocoa/tabs/tab_view.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_view.h"
 
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 201 matching lines @@
   // Cancel any delayed requests that may still be pending (drags or hover).
   [NSObject cancelPreviousPerformRequestsWithTarget:self];
   if (&NSWorkspaceAccessibilityDisplayOptionsDidChangeNotification) {
     NSNotificationCenter* center =
         [[NSWorkspace sharedWorkspace] notificationCenter];
     [center removeObserver:self];
   }
   [super dealloc];
 }
 
+// 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.
+- (NSRect)_opaqueRectForWindowMoveWhenInTitlebar {
+  return [self bounds];
+}
+
 // Called to obtain the context menu for when the user hits the right mouse
 // button (or control-clicks). (Note that -rightMouseDown: is *not* called for
 // control-click.)
 - (NSMenu*)menu {
   if ([self isClosing])
     return nil;
 
   return [controller_ menu];
 }
 
@@ skipping 770 matching lines @@
 
 // For "Increase Contrast" mode, use flat black instead of semitransparent black
 // for the tab edge stroke.
 + (void)setTabEdgeStrokeColor {
   static NSColor* heavyStrokeColor =
       [skia::SkColorToSRGBNSColor(SK_ColorBLACK) retain];
   [heavyStrokeColor set];
 }
 
 @end