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

content/browser/download/download_manager.cc

Index: content/browser/download/download_manager.cc
diff --git a/content/browser/download/download_manager.cc b/content/browser/download/download_manager.cc
index e56a92791a4d8e498195d9e8569d3c447b3ac1da..99b8d614d0939eb3e0aa8f6719d4057c47f7c003 100644
--- a/content/browser/download/download_manager.cc
+++ b/content/browser/download/download_manager.cc
@@ -20,7 +20,7 @@
 #include "content/browser/download/download_create_info.h"
 #include "content/browser/download/download_file_manager.h"
 #include "content/browser/download/download_id_factory.h"
-#include "content/browser/download/download_item.h"
+#include "content/browser/download/download_item_impl.h"
 #include "content/browser/download/download_persistent_store_info.h"
 #include "content/browser/download/download_stats.h"
 #include "content/browser/download/download_status_updater.h"
@@ -318,7 +318,7 @@ void DownloadManager::CreateDownloadItem(
     DownloadCreateInfo* info, const DownloadRequestHandle& request_handle) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  DownloadItem* download = new DownloadItem(
+  DownloadItem* download = new DownloadItemImpl(
       this, *info, new DownloadRequestHandle(request_handle),
       browser_context_->IsOffTheRecord());
   int32 download_id = info->download_id.local();
@@ -819,7 +819,7 @@ void DownloadManager::OnPersistentStoreQueryComplete(
   largest_db_handle_in_history_ = 0;
 
   for (size_t i = 0; i < entries->size(); ++i) {
-    DownloadItem* download = new DownloadItem(this, entries->at(i));
+    DownloadItem* download = new DownloadItemImpl(this, entries->at(i));
     // TODO(rdsmith): Remove after http://crbug.com/85408 resolved.
     CHECK(!ContainsKey(history_downloads_, download->db_handle()));
     downloads_.insert(download);