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

content/shell/shell_download_manager_delegate.cc

Index: content/shell/shell_download_manager_delegate.cc
diff --git a/content/shell/shell_download_manager_delegate.cc b/content/shell/shell_download_manager_delegate.cc
index 718ae3b4f78b0f5b6917e2ab53cd988e4122db09..f1f58fe9c6682cc5aee6fb9a43dc393d04482e9d 100644
--- a/content/shell/shell_download_manager_delegate.cc
+++ b/content/shell/shell_download_manager_delegate.cc
@@ -42,17 +42,17 @@ void ShellDownloadManagerDelegate::Shutdown() {
 bool ShellDownloadManagerDelegate::ShouldStartDownload(int32 download_id) {
   DownloadItem* download =
       download_manager_->GetActiveDownloadItem(download_id);
-  DownloadStateInfo state = download->state_info();
+  DownloadStateInfo state = download->GetStateInfo();
 
   if (!state.force_file_name.empty())
     return true;
 
   FilePath generated_name = net::GenerateFileName(
       download->GetURL(),
-      download->content_disposition(),
-      download->referrer_charset(),
-      download->suggested_filename(),
-      download->mime_type(),
+      download->GetContentDisposition(),
+      download->GetReferrerCharset(),
+      download->GetSuggestedFilename(),
+      download->GetMimeType(),
       "download");
 
   // Since we have no download UI, show the user a dialog always.