Remove ability to switch to pre-MD UI from about:flags.

chrome/browser/ui/layout_constants.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_UI_LAYOUT_CONSTANTS_H_
 #define CHROME_BROWSER_UI_LAYOUT_CONSTANTS_H_
 
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/geometry/size.h"
 
@@ skipping 13 matching lines @@
 
   // The additional vertical padding of a bubble.
   LOCATION_BAR_BUBBLE_VERTICAL_PADDING,
 
   // The vertical inset to apply to the bounds of a location bar bubble's anchor
   // view, to bring the bubble closer to the anchor.  This compensates for the
   // space between the bottoms of most such views and the visible bottoms of the
   // images inside.
   LOCATION_BAR_BUBBLE_ANCHOR_VERTICAL_INSET,
 
-  // The height to be occupied by the LocationBar. For
-  // MaterialDesignController::NON_MATERIAL the height is determined from image
-  // assets.
+  // The height to be occupied by the LocationBar.
   LOCATION_BAR_HEIGHT,
 
   // Space between items in the location bar, as well as between items and the
   // edges.
   LOCATION_BAR_HORIZONTAL_PADDING,
 
   // Space between the location bar edge and contents.
   LOCATION_BAR_VERTICAL_PADDING,
 
   // The number of pixels in the omnibox dropdown border image interior to
@@ skipping 83 matching lines @@
   // The visible size of the new tab button; does not include any Fitts' Law
   // extensions.
   NEW_TAB_BUTTON,
 };
 
 int GetLayoutConstant(LayoutConstant constant);
 gfx::Insets GetLayoutInsets(LayoutInset inset);
 gfx::Size GetLayoutSize(LayoutSize size);
 
 #endif  // CHROME_BROWSER_UI_LAYOUT_CONSTANTS_H_