[Mac] Avoid "adding unknown subview" warning.

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

Index: chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
diff --git a/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm b/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
index e8465ef4a9b2b78128128a98cc057b19917586c3..714dd954e318e3cb9ae157517a53b3d03d56c3b5 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
@@ -395,9 +395,13 @@
   [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]];