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

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 <uxtheme.h>
 #include <vsstyle.h>
 #include <vssym32.h>
@@ skipping 55 matching lines @@
   COLOR_GRAYTEXT,
   COLOR_HIGHLIGHT,
   COLOR_HIGHLIGHTTEXT,
   COLOR_SCROLLBAR,
   COLOR_WINDOW,
   COLOR_WINDOWTEXT,
   COLOR_BTNFACE,
   COLOR_MENUHIGHLIGHT,
 };
 
+const int kUnthemedScrollbarThickness =
+    static_cast<int>(GetSystemMetrics(SM_CXVSCROLL) /

[sky, 2013/02/20 22:22:47]

Can't GetSystemMetrics change?

[kevers, 2013/02/20 22:37:22]

The system metric could change if you update your theme while running chrome;
however, checking the system metric for each part size call would reintroduce
the perf regression.

A bit of background...  WebKit used to pick up the scrollbar with a single call
to GetSystemMetrics and cache the value.  The problem is that the system metrics
is in pixels and WebKit in DIP.  Thus, we got fat scrollbars in Windows when
using high-DPI mode.  This fix addresses the fat scrollbars problem, while
retaining much of the efficiency that we had earlier in the WebKit
implementation by using a cached value.  Seems like a reasonable compromise.

[sky, 2013/02/20 22:59:00]

When that happens don't we get a WM_SYSCOLORCHANGE? You should make this a
member and update it when the system colors changes.

+                     ui::win::GetDeviceScaleFactor());
+
 void SetCheckerboardShader(SkPaint* paint, const RECT& align_rect) {
   // Create a 2x2 checkerboard pattern using the 3D face and highlight colors.
   const SkColor face = color_utils::GetSysSkColor(COLOR_3DFACE);
   const SkColor highlight = color_utils::GetSysSkColor(COLOR_3DHILIGHT);
   SkColor buffer[] = { face, highlight, highlight, face };
   // Confusing bit: we first create a temporary bitmap with our desired pattern,
   // then copy it to another bitmap.  The temporary bitmap doesn't take
   // ownership of the pixel data, and so will point to garbage when this
   // function returns.  The copy will copy the pixel data into a place owned by
   // the bitmap, which is in turn owned by the shader, etc., so it will live
@@ skipping 161 matching lines @@
     // when theming is not enabled.  Support for other parts can be added
     // if/when needed.
     switch (part) {
       case kCheckbox:
       case kRadio:
         // TODO(rogerta): I was not able to find any API to get the default
         // size of these controls, so determined these values empirically.
         size.cx = 13;
         size.cy = 13;
         break;
+      case kScrollbarDownArrow:
+      case kScrollbarLeftArrow:
+      case kScrollbarRightArrow:
+      case kScrollbarUpArrow:
+      case kScrollbarHorizontalThumb:
+      case kScrollbarVerticalThumb:
+        size.cx = size.cy = kUnthemedScrollbarThickness;
+        break;
       default:
         size.cx = 0;
         size.cy = 0;
         break;
     }
   }
 
   return gfx::Size(size.cx, size.cy);
 }
 
@@ skipping 1790 matching lines @@
     handle = open_theme_(NULL, L"Spin");
     break;
   default:
     NOTREACHED();
   }
   theme_handles_[theme_name] = handle;
   return handle;
 }
 
 }  // namespace ui