Add "dangerous download" view on OS X, for now for dmg files. Also fix download item layout.

chrome/browser/download/download_exe.cc

 // Copyright (c) 2006-2008 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 <set>
 #include <string>
 
 #include "chrome/browser/download/download_util.h"
 
 #include "base/logging.h"
@@ skipping 127 matching lines @@
   "xht",
   "xhtm",
   "xhtml",
 #elif defined(OS_LINUX)
   // TODO(estade): lengthen this list.
   "exe",
   "pl",
   "py",
   "rb",
   "sh",
-#endif  // defined(OS_LINUX)
+#elif defined(OS_MACOSX)
+  // TODO(thakis): Figure out what makes sense here -- crbug.com/19096
+  "dmg",
+#endif
 };
 
 void InitializeExeTypes(std::set<std::string>* exe_extensions) {
   DCHECK(exe_extensions);
   for (size_t i = 0; i < arraysize(g_executables); ++i)
     exe_extensions->insert(g_executables[i]);
 }
 
 }  // namespace download_util