Get rid of ScrollbarGroup. Sky doesn't use it.

sky/engine/web/BUILD.gn

 # Copyright 2014 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("//build/config/ui.gni")
 import("//sky/engine/config.gni")
 
 visibility = ["//sky/*"]
 
 platform_web_unittest_files = [
@@ skipping 32 matching lines @@
     "EditorClientImpl.cpp",
     "EditorClientImpl.h",
     "FrameLoaderClientImpl.cpp",
     "FrameLoaderClientImpl.h",
     "GraphicsLayerFactoryChromium.cpp",
     "GraphicsLayerFactoryChromium.h",
     "LinkHighlight.cpp",
     "LinkHighlight.h",
     "PageWidgetDelegate.cpp",
     "PageWidgetDelegate.h",
-    "ScrollbarGroup.cpp",
-    "ScrollbarGroup.h",
     "SpellCheckerClientImpl.cpp",
     "SpellCheckerClientImpl.h",
     "ViewportAnchor.cpp",
     "ViewportAnchor.h",
     "WebArrayBufferConverter.cpp",
     "WebArrayBufferView.cpp",
     "WebCache.cpp",
     "WebCachedURLRequest.cpp",
     "WebColorSuggestion.cpp",
     "WebCustomElement.cpp",
@@ skipping 115 matching lines @@
   configs += [ "//sky/engine:config" ]
 
   if (!is_component_build) {
     deps += [ "//sky/engine/core" ]
 
     configs += [ "//sky/engine:inside_blink" ]
 
     sources += platform_web_unittest_files
   }
 }