Implemented ExternalData interface on DownloadItem and used it for SafeBrowsing.

content/browser/download/download_item.cc

Index: content/browser/download/download_item.cc
diff --git a/content/browser/download/download_item.cc b/content/browser/download/download_item.cc
index e3eff9943cf34b37c35f0b76a1f26125076bdb2f..bc2a278da8c54b7812c139320307cc77149c7d08 100644
--- a/content/browser/download/download_item.cc
+++ b/content/browser/download/download_item.cc
@@ -14,6 +14,7 @@
 #include "base/i18n/string_search.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
+#include "base/stl_util.h"
 #include "base/stringprintf.h"
 #include "base/utf_string_conversions.h"
 #include "content/browser/download/download_create_info.h"
@@ -233,6 +234,8 @@ DownloadItem::~DownloadItem() {
 
   TransitionTo(REMOVING);
   download_manager_->AssertQueueStateConsistent(this);
+  STLDeleteContainerPairSecondPointers(
+      external_data_map_.begin(), external_data_map_.end());
 }
 
 void DownloadItem::AddObserver(Observer* observer) {
@@ -716,6 +719,23 @@ void DownloadItem::OffThreadCancel(DownloadFileManager* file_manager) {
                                      file_manager, global_id()));
 }
 
+DownloadItem::ExternalData*
+DownloadItem::GetExternalData(void* key) {
+  if (external_data_map_.count(key) == 0)
+    return NULL;
+  return external_data_map_[key];
+}
+
+void DownloadItem::SetExternalData(
+    void* key, DownloadItem::ExternalData* data) {
+  if (external_data_map_.count(key) != 0) {

[noelutz, 2011/11/16 02:59:38]

How about this to avoid all these lookups?

std::map<void*, ExternalData*>::iterator it = ....find(key);
if (it == ...end()) {
  external_data_map_[key] = data;
} else if (it->second != data) {
  delete it->second;
  it->second = data;
}

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

Yes, noticeably better.  Thanks for the nudge.  Done.

+    if (external_data_map_[key] == data)
+      return;                           // Nothing to do.
+    delete external_data_map_[key];
+  }
+  external_data_map_[key] = data;
+}
+
 void DownloadItem::Init(bool active) {
   // TODO(rdsmith): Change to DCHECK after http://crbug.com/85408 resolved.
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));