[Mac] Avoid "adding unknown subview" warning.

chrome/browser/ui/cocoa/tabs/tab_window_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_window_controller.h"
 
 #include "base/logging.h"
 #import "base/mac/sdk_forward_declarations.h"
 #import "chrome/browser/ui/cocoa/browser_window_layout.h"
 #import "chrome/browser/ui/cocoa/fast_resize_view.h"
@@ skipping 377 matching lines @@
   // the start of -[BrowserWindowController initWithBrowser:takeOwnership:],
   // before the |browser_| ivar has been set. Without a browser object we
   // can't check the window's theme. The final setup happens in
   // -[TabStripView setController:], at which point we have access to the theme.
   [visualEffectView setAppearance:
       [NSAppearance appearanceNamed:NSAppearanceNameVibrantLight]];
   [visualEffectView setMaterial:NSVisualEffectMaterialLight];
   [visualEffectView setBlendingMode:NSVisualEffectBlendingModeBehindWindow];
   [visualEffectView setState:NSVisualEffectStateFollowsWindowActiveState];
 
-  [rootView addSubview:visualEffectView
-            positioned:NSWindowBelow
-            relativeTo:nil];
+  if (base::mac::IsAtMostOS10_10()) {
+    [rootView addSubview:visualEffectView
+              positioned:NSWindowBelow
+              relativeTo:nil];
+  } else {
+    [[window contentView] addSubview:visualEffectView];
+  }
 
   // Make the |tabStripBackgroundView_| a child of the NSVisualEffectView.
   [tabStripBackgroundView_ setFrame:[visualEffectView bounds]];
   [visualEffectView addSubview:tabStripBackgroundView_];
 }
 
 // Called when the size of the window content area has changed. Override to
 // position specific views. Base class implementation does nothing.
 - (void)layoutSubviews {
   NOTIMPLEMENTED();
 }
 
 @end