Implemented ExternalData interface on DownloadItem and used it for SafeBrowsing.

content/browser/download/download_item.h

Index: content/browser/download/download_item.h
diff --git a/content/browser/download/download_item.h b/content/browser/download/download_item.h
index 3d3b0e7ace3a8b7454f1f7cc31088b3a2c5cc6e7..bc1f9657ad636b8aaa220b9c4da8f4d13fade13a 100644
--- a/content/browser/download/download_item.h
+++ b/content/browser/download/download_item.h
@@ -18,6 +18,7 @@
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ITEM_H_
 #pragma once
 
+#include <map>
 #include <string>
 
 #include "base/basictypes.h"
@@ -117,6 +118,13 @@ class CONTENT_EXPORT DownloadItem {
     virtual ~Observer() {}
   };
 
+  // Interface for data that can be stored associated with (and owned
+  // by) an object of this class via GetExternalData/SetExternalData.
+  class ExternalData {
+   public:
+    virtual ~ExternalData() {};
+  };
+
   // Constructing from persistent store:
   DownloadItem(DownloadManager* download_manager,
                const DownloadPersistentStoreInfo& info);
@@ -349,6 +357,20 @@ class CONTENT_EXPORT DownloadItem {
 
   void MockDownloadOpenForTesting() { open_enabled_ = false; }
 
+  // Manage data owned by other subsystems associated with the
+  // DownloadItem.  By custom, key is the address of a
+  // static char subsystem_specific_string[] = ".."; defined
+  // in the subsystem, but the only requirement of this interface
+  // is that the key be unique over all data stored with this
+  // DownloadItem.
+  //
+  // Note that SetExternalData takes ownership of the
+  // passed object; it will be destroyed when the DownloadItem is.
+  // If an object is already held by the DownloadItem associated with
+  // the passed key, it will be destroyed on overwrite.
+  ExternalData* GetExternalData(void* key);
+  void SetExternalData(void* key, ExternalData* data);
+
  private:
   // Construction common to all constructors. |active| should be true for new
   // downloads and false for downloads from the history.
@@ -492,6 +514,10 @@ class CONTENT_EXPORT DownloadItem {
   // Did the delegate delay calling Complete on this download?
   bool delegate_delayed_complete_;
 
+  // External Data storage.  All objects in the store
+  // are owned by the DownloadItem.
+  std::map<void*, ExternalData*> external_data_map_;

[asanka, 2011/11/16 03:52:19]

Would a std::map<const void*, ExternalData*> be better?

[Randy Smith (Not in Mondays), 2011/11/18 02:02:57]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(DownloadItem);
 };