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

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..b70bbcdfa42b1417158c31febb46ab8fca742e39 100644
--- a/content/shell/shell_download_manager_delegate.cc
+++ b/content/shell/shell_download_manager_delegate.cc
@@ -72,7 +72,7 @@ void ShellDownloadManagerDelegate::GenerateFilename(
     DownloadStateInfo state,
     const FilePath& generated_name) {
   if (state.suggested_path.empty()) {
-    state.suggested_path = download_manager_->browser_context()->GetPath().
+    state.suggested_path = download_manager_->BrowserContext()->GetPath().
         Append(FILE_PATH_LITERAL("Downloads"));
     if (!file_util::PathExists(state.suggested_path))
       file_util::CreateDirectory(state.suggested_path);