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

chrome/browser/cocoa/download_item_mac.h

Index: chrome/browser/cocoa/download_item_mac.h
diff --git a/chrome/browser/cocoa/download_item_mac.h b/chrome/browser/cocoa/download_item_mac.h
index f992e21a90ce441cfb0ac1b9168b9c3c6dad519d..a7f41a8563ebd34361b6c697830745e70827f1e8 100644
--- a/chrome/browser/cocoa/download_item_mac.h
+++ b/chrome/browser/cocoa/download_item_mac.h
@@ -51,6 +51,9 @@ class DownloadItemMac : DownloadItem::Observer {
   // For canceling an in progress icon request.
   CancelableRequestConsumerT<int, 0> icon_consumer_;
 
+  // Stores the last known name where the file will be saved.
+  FilePath lastFilePath_;
+
   DISALLOW_COPY_AND_ASSIGN(DownloadItemMac);
 };