Make download items drag sources on OS X.

chrome/browser/cocoa/download_item_button_unittest.mm

+// Copyright (c) 2010 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 "base/scoped_nsobject.h"
+#import "chrome/browser/cocoa/download_item_button.h"
+#import "chrome/browser/cocoa/cocoa_test_helper.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "testing/platform_test.h"
+
+// Make sure nothing leaks.
+TEST(DownloadItemButtonTest, Create) {
+  scoped_nsobject<DownloadItemButton> button;
+  button.reset([[DownloadItemButton alloc]
+      initWithFrame:NSMakeRect(0,0,500,500)]);
+
+  // Test setter
+  FilePath path("foo");
+  [button.get() setDownload:path];
+  EXPECT_EQ(path.value(), [button.get() download].value());
+}