Created a DownloadManager interface, for use in unit tests..

chrome/browser/download/download_file_picker.h

Index: chrome/browser/download/download_file_picker.h
diff --git a/chrome/browser/download/download_file_picker.h b/chrome/browser/download/download_file_picker.h
index bd665a892a6e52aebd427cec7d95d985e4725eff..52ce4a7298ab4de075a52217ecaa4008f0359d2a 100644
--- a/chrome/browser/download/download_file_picker.h
+++ b/chrome/browser/download/download_file_picker.h
@@ -16,7 +16,7 @@ class TabContents;
 class DownloadFilePicker : public DownloadManager::Observer,
                            public SelectFileDialog::Listener {
  public:
-  DownloadFilePicker(DownloadManager* download_manager,
+  DownloadFilePicker(DownloadManagerInterface* download_manager,
                      TabContents* tab_contents,
                      const FilePath& suggested_path,
                      void* params);
@@ -31,7 +31,7 @@ class DownloadFilePicker : public DownloadManager::Observer,
   virtual void FileSelected(const FilePath& path, int index, void* params);
   virtual void FileSelectionCanceled(void* params);
 
-  DownloadManager* download_manager_;
+  DownloadManagerInterface* download_manager_;
 
   // For managing select file dialogs.
   scoped_refptr<SelectFileDialog> select_file_dialog_;