Split DownloadItem into an ABC, an Impl, and a Mock.

content/browser/download/save_package.cc

Index: content/browser/download/save_package.cc
diff --git a/content/browser/download/save_package.cc b/content/browser/download/save_package.cc
index a0dca3bc9d88cd4fc379d2ea69d961a741641694..7e84b0de2bf05920858a0ddbe67937670eb8f01c 100644
--- a/content/browser/download/save_package.cc
+++ b/content/browser/download/save_package.cc
@@ -20,7 +20,7 @@
 #include "base/utf_string_conversions.h"
 #include "content/browser/browser_context.h"
 #include "content/browser/download/download_file_manager.h"
-#include "content/browser/download/download_item.h"
+#include "content/browser/download/download_item_impl.h"
 #include "content/browser/download/download_manager.h"
 #include "content/browser/download/save_file.h"
 #include "content/browser/download/save_file_manager.h"
@@ -266,11 +266,11 @@ bool SavePackage::Init() {
   }
 
   // Create the download item, and add ourself as an observer.
-  download_ = new DownloadItem(download_manager_,
-                               saved_main_file_path_,
-                               page_url_,
-                               browser_context->IsOffTheRecord(),
-                               download_manager_->GetNextId());
+  download_ = new DownloadItemImpl(download_manager_,
+                                   saved_main_file_path_,
+                                   page_url_,
+                                   browser_context->IsOffTheRecord(),
+                                   download_manager_->GetNextId());
   download_->AddObserver(this);
 
   // Transfer ownership to the download manager.