Fix scrollbar transparency / opacity issues on Windows.

ui/base/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/base/native_theme/native_theme_win.h"
 
 #include <windows.h>
 #include <uxtheme.h>
 #include <vsstyle.h>
 #include <vssym32.h>
@@ skipping 269 matching lines @@
   }
 
   return gfx::Size(size.cx, size.cy);
 }
 
 void NativeThemeWin::Paint(SkCanvas* canvas,
                            Part part,
                            State state,
                            const gfx::Rect& rect,
                            const ExtraParams& extra) const {
+  bool needs_paint_indirect = false;
   if (!skia::SupportsPlatformPaint(canvas)) {
     // This block will only get hit with --enable-accelerated-drawing flag.
-    PaintToNonPlatformCanvas(canvas, part, state, rect, extra);
-    return;
+    needs_paint_indirect = true;
+  } else {
+    // Scrollbars on Windows XP and the Windows Classic theme have particularly
+    // problematic alpha values, so always draw them indirectly.
+    switch (part) {
+      case kScrollbarDownArrow:
+      case kScrollbarUpArrow:
+      case kScrollbarLeftArrow:
+      case kScrollbarRightArrow:
+      case kScrollbarHorizontalThumb:
+      case kScrollbarVerticalThumb:
+      case kScrollbarHorizontalGripper:
+      case kScrollbarVerticalGripper:
+        if (!GetThemeHandle(SCROLLBAR))
+          needs_paint_indirect = true;
+        break;
+      default:
+        break;
+    }
   }
 
+  if (needs_paint_indirect)
+    PaintIndirect(canvas, part, state, rect, extra);
+  else
+    PaintDirect(canvas, part, state, rect, extra);
+}
+
+void NativeThemeWin::PaintDirect(SkCanvas* canvas,
+                                 Part part,
+                                 State state,
+                                 const gfx::Rect& rect,
+                                 const ExtraParams& extra) const {
   skia::ScopedPlatformPaint scoped_platform_paint(canvas);
   HDC hdc = scoped_platform_paint.GetPlatformSurface();
 
   switch (part) {
     case kCheckbox:
       PaintCheckbox(hdc, part, state, rect, extra.button);
       break;
     case kRadio:
       PaintRadioButton(hdc, part, state, rect, extra.button);
       break;
@@ skipping 127 matching lines @@
     case kColorId_TextfieldSelectionBackgroundUnfocused:
       return kTextfieldSelectionBackgroundUnfocused;
 
     default:
       NOTREACHED() << "Invalid color_id: " << color_id;
       break;
   }
   return kInvalidColorIdColor;
 }
 
-void NativeThemeWin::PaintToNonPlatformCanvas(SkCanvas* canvas,
-                                              Part part,
-                                              State state,
-                                              const gfx::Rect& rect,
-                                              const ExtraParams& extra) const {
+void NativeThemeWin::PaintIndirect(SkCanvas* 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.
 
   // Create an offscreen canvas that is backed by an HDC.
   scoped_ptr<SkCanvas> offscreen_canvas(
       skia::CreateBitmapCanvas(rect.width(), rect.height(), false));
   DCHECK(offscreen_canvas.get());
   DCHECK(skia::SupportsPlatformPaint(offscreen_canvas.get()));
@@ skipping 17 matching lines @@
       adjusted_extra.progress_bar.value_rect_y = 0;
       break;
     case kScrollbarHorizontalTrack:
     case kScrollbarVerticalTrack:
       adjusted_extra.scrollbar_track.track_x = 0;
       adjusted_extra.scrollbar_track.track_y = 0;
       break;
     default: break;
   }
   // Draw the theme controls using existing HDC-drawing code.
-  Paint(offscreen_canvas.get(), part, state, adjusted_rect, adjusted_extra);
+  PaintDirect(offscreen_canvas.get(),
+              part,
+              state,
+              adjusted_rect,
+              adjusted_extra);
 
   // Copy the pixels to a bitmap that has ref-counted pixel storage, which is
   // necessary to have when drawing to a SkPicture.
   const SkBitmap& hdc_bitmap =
       offscreen_canvas->getDevice()->accessBitmap(false);
   SkBitmap bitmap;
   hdc_bitmap.copyTo(&bitmap, SkBitmap::kARGB_8888_Config);
 
   // Post-process the pixels to fix up the alpha values (see big comment above).
   const SkPMColor placeholder_value = SkPreMultiplyColor(placeholder);
@@ skipping 1280 matching lines @@
     handle = open_theme_(NULL, L"Spin");
     break;
   default:
     NOTREACHED();
   }
   theme_handles_[theme_name] = handle;
   return handle;
 }
 
 }  // namespace ui