Use nine-patch resource for drawing Aura overlay scrollbar thumb.

ui/native_theme/native_theme_win.cc

 // 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.
 
 #include "ui/native_theme/native_theme_win.h"
 
 #include <windows.h>
 #include <stddef.h>
 #include <uxtheme.h>
 #include <vsstyle.h>
@@ skipping 642 matching lines @@
       case NativeTheme::kColorId_ProminentButtonColor:
         return kProminentButtonColorInvert;
       default:
         return color_utils::InvertColor(GetAuraColor(color_id, this));
     }
   }
 
   return GetAuraColor(color_id, this);
 }
 
+bool NativeThemeWin::SupportsNinePatch(Part part) const {
+  return false;

[sadrul, 2017/03/01 15:38:55]

We are using the same compositor on windows. Why would it not support nine-patch
layer?

[bokan, 2017/03/01 16:22:45]

Only the scrollbar thumb for overlay scrollbars will now be a nine-patch.
That'll only be used on CrOS in stable, but even on windows if enabled via flag,
the overlay scrollbar thumb is painted by native_theme_aura (as is all Web
content). I've added a comment here to make that clearer.

+}
+
+gfx::Size NativeThemeWin::GetNinePatchCanvasSize(Part part) const {
+  NOTREACHED() << "NativeThemeWin doesn't support nine-patch resources.";
+  return gfx::Size();
+}
+
+gfx::Rect NativeThemeWin::GetNinePatchAperture(Part part) const {
+  NOTREACHED() << "NativeThemeWin doesn't support nine-patch resources.";
+  return gfx::Rect();
+}
+
 void NativeThemeWin::PaintIndirect(cc::PaintCanvas* destination_canvas,
                                    Part part,
                                    State state,
                                    const gfx::Rect& rect,
                                    const ExtraParams& extra) const {
   // TODO(asvitkine): This path is pretty inefficient - for each paint operation
   // it creates a new offscreen bitmap Skia canvas. This can be sped up by doing
   // it only once per part/state and keeping a cache of the resulting bitmaps.
   //
   // TODO(enne): This could also potentially be sped up for software raster
@@ skipping 1419 matching lines @@
     break;
   case LAST:
     NOTREACHED();
     break;
   }
   theme_handles_[theme_name] = handle;
   return handle;
 }
 
 }  // namespace ui