cocoa browser: remove non-material tabstrip support

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..0d1927f1bee471859e4aacc843fa6e9f524893ab 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
@@ -359,8 +359,7 @@ - (void)insertTabStripBackgroundViewIntoWindow:(NSWindow*)window
   // In Material Design on 10.10 and higher, the top portion of the window is
   // blurred using an NSVisualEffectView.
   Class nsVisualEffectViewClass = NSClassFromString(@"NSVisualEffectView");
-  if (!ui::MaterialDesignController::IsModeMaterial() ||
-      !nsVisualEffectViewClass) {
+  if (!nsVisualEffectViewClass) {
     [rootView addSubview:tabStripBackgroundView_
               positioned:NSWindowBelow
               relativeTo:nil];