cocoa browser: remove non-material tabstrip support

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 341 matching lines @@
 }
 
 - (void)insertTabStripBackgroundViewIntoWindow:(NSWindow*)window
                                       titleBar:(BOOL)hasTitleBar {
   DCHECK(tabStripBackgroundView_);
   NSView* rootView = [[window contentView] superview];
 
   // 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];
     return;
   }
 
   [window setTitlebarAppearsTransparent:YES];
 
   // If the window has a normal titlebar, then do not add NSVisualEffectView.
   if (hasTitleBar)
@@ skipping 30 matching lines @@
   [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