Merge 122791 - [chromium] Turn off ScrollbarLayerChromium for Windows due to bad alpha values

Source/WebCore/page/scrolling/chromium/ScrollingCoordinatorChromium.cpp

Index: Source/WebCore/page/scrolling/chromium/ScrollingCoordinatorChromium.cpp
===================================================================
--- Source/WebCore/page/scrolling/chromium/ScrollingCoordinatorChromium.cpp	(revision 122853)
+++ Source/WebCore/page/scrolling/chromium/ScrollingCoordinatorChromium.cpp	(working copy)
@@ -120,9 +120,12 @@
     if (!scrollbarGraphicsLayer->contentsOpaque())
         scrollbarGraphicsLayer->setContentsOpaque(isOpaqueRootScrollbar);
 
-    // FIXME: Mac scrollbar themes are not thread-safe.
+    // FIXME: Mac scrollbar themes are not thread-safe to paint.
+    // FIXME: Win scrollbars on XP Classic themes do not paint valid alpha
+    // values due to GDI. This needs to be fixed in theme code before it
+    // can be turned on here.
     bool platformSupported = true;
-#if OS(DARWIN)
+#if OS(DARWIN) || OS(WINDOWS)
     platformSupported = false;
 #endif