Fix the size of scrollbars when using the Windows Classic theme.

webkit/glue/webthemeengine_impl_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 "webkit/glue/webthemeengine_impl_win.h"
 
 #include <vsstyle.h>  // To convert to ui::NativeTheme::State
 
 #include "base/logging.h"
 #include "skia/ext/platform_canvas.h"
 #include "skia/ext/skia_utils_win.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebRect.h"
+#include "ui/base/win/dpi.h"
 #include "ui/native_theme/native_theme.h"
 
 using WebKit::WebCanvas;
 using WebKit::WebColor;
 using WebKit::WebRect;
 using WebKit::WebSize;
 
 namespace webkit_glue {
 
 static RECT WebRectToRECT(const WebRect& rect) {
@@ skipping 962 matching lines @@
                                       extra);
 }
 
 WebSize WebThemeEngineImpl::getSize(int part) {
   switch (part) {
     case SBP_ARROWBTN: {
       gfx::Size size = ui::NativeTheme::instance()->GetPartSize(
           ui::NativeTheme::kScrollbarUpArrow,
           ui::NativeTheme::kNormal,
           ui::NativeTheme::ExtraParams());
+      // Part size retrieval can fail with the Windows Classic theme.

[tony, 2013/02/21 18:46:26]

Does it always fail when using the Windows Classic theme?  It would be nice if
this comment explained why this happens.

[kevers, 2013/02/21 19:12:23]

Updated comment.  Yes, the size of a scrollbar button is always returned as (0,
0) if not using a themed style and Windows Classic theme falls into this
category.

+      if(size.width() == 0) {

[tony, 2013/02/21 18:46:26]

Nit: Space missing after "if".

[kevers, 2013/02/21 19:12:23]

Fixed.

+        int width = static_cast<int>(GetSystemMetrics(SM_CXVSCROLL) /
+            ui::win::GetDeviceScaleFactor());
+        size = gfx::Size(width, width);
+      }
       return WebSize(size.width(), size.height());
     }
     default:
       NOTREACHED() << "Unhandled part: " << part;
   }
   return WebSize();
 }
 
 }  // namespace webkit_glue