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

webkit/glue/webthemeengine_impl_win.cc

Index: webkit/glue/webthemeengine_impl_win.cc
diff --git a/webkit/glue/webthemeengine_impl_win.cc b/webkit/glue/webthemeengine_impl_win.cc
index 132345b253accc07cb8a3240e2adf0ce4d02fc35..b201bba95e2ba1c9edc969f443c816ce7e474268 100644
--- a/webkit/glue/webthemeengine_impl_win.cc
+++ b/webkit/glue/webthemeengine_impl_win.cc
@@ -10,6 +10,7 @@
 #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;
@@ -992,6 +993,12 @@ WebSize WebThemeEngineImpl::getSize(int part) {
           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: