Mac: Draw download item background like windows does if a theme is installed.

chrome/browser/cocoa/download_item_cell.h

Index: chrome/browser/cocoa/download_item_cell.h
diff --git a/chrome/browser/cocoa/download_item_cell.h b/chrome/browser/cocoa/download_item_cell.h
index 3c2b7d59ff765e45a113fcb6c2e7b928dbefb3e2..248225c0c20b1895593c42b5ad14552d8eb72179 100644
--- a/chrome/browser/cocoa/download_item_cell.h
+++ b/chrome/browser/cocoa/download_item_cell.h
@@ -11,6 +11,7 @@
 #include "base/file_path.h"
 
 class BaseDownloadItemModel;
+@class GTMTheme;
 
 // A button cell that implements the weird button/popup button hybrid that is
 // used by the download items.
@@ -42,6 +43,8 @@ enum DownloadItemMousePosition {
   CGFloat titleY_;
   CGFloat statusAlpha_;
   scoped_nsobject<NSAnimation> hideStatusAnimation_;
+
+  scoped_nsobject<GTMTheme> theme_;
 }
 
 - (void)setStateFromDownload:(BaseDownloadItemModel*)downloadModel;