[Mac] Avoid "adding unknown subview" warning.

chrome/browser/ui/cocoa/tabs/tab_strip_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_strip_view.h"
 
 #include <cmath>  // floor
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
@@ skipping 360 matching lines @@
 }
 
 - (NSVisualEffectView*)visualEffectView {
   // NSVisualEffectView is only used in Material Design, and only available on
   // OS X 10.10 and higher.
   if (!ui::MaterialDesignController::IsModeMaterial() ||
       !base::mac::IsAtLeastOS10_10()) {
     return nil;
   }
 
-  NSView* rootView = [[[self window] contentView] superview];
+  NSView* rootView = [[self window] contentView];
+  if (base::mac::IsAtMostOS10_10()) {
+    rootView = [rootView superview];
+  }
+
   Class nsVisualEffectViewClass = NSClassFromString(@"NSVisualEffectView");
   DCHECK(nsVisualEffectViewClass);
   for (NSView* view in [rootView subviews]) {
     if ([view isKindOfClass:nsVisualEffectViewClass]) {
       return base::mac::ObjCCast<NSVisualEffectView>(view);
     }
   }
   return nil;
 }
 
@@ skipping 52 matching lines @@
   if (visualEffectsDisabledForFullscreen_ ||
       themeProvider->HasCustomImage(IDR_THEME_FRAME) ||
       themeProvider->HasCustomColor(ThemeProperties::COLOR_FRAME)) {
     [visualEffectView setState:NSVisualEffectStateInactive];
   } else {
     [visualEffectView setState:NSVisualEffectStateFollowsWindowActiveState];
   }
 }
 
 @end