Add resource ID based download requests in {GDataWapi/Drive} requests.

chrome/browser/google_apis/drive_api_requests.h

Index: chrome/browser/google_apis/drive_api_requests.h
diff --git a/chrome/browser/google_apis/drive_api_requests.h b/chrome/browser/google_apis/drive_api_requests.h
index 1afa8c1f4c6d5d1e2f6502f4f48b55b4c2a296c3..0fa5a7953e6e5874f3cb555673b60270ec695325 100644
--- a/chrome/browser/google_apis/drive_api_requests.h
+++ b/chrome/browser/google_apis/drive_api_requests.h
@@ -528,6 +528,23 @@ class GetUploadStatusRequest : public GetUploadStatusRequestBase {
   DISALLOW_COPY_AND_ASSIGN(GetUploadStatusRequest);
 };
 
+//========================== DownloadFileRequest ==========================
+
+// This class performs the request for downloading of a specified file.
+class DownloadFileRequest : public DownloadFileRequestBase {
+ public:
+  // See also DownloadFileRequestBase's comment for parameters meaning.
+  DownloadFileRequest(RequestSender* sender,
+                      const DriveApiUrlGenerator& url_generator,
+                      const std::string& resource_id,
+                      const base::FilePath& output_file_path,
+                      const DownloadActionCallback& download_action_callback,
+                      const GetContentCallback& get_content_callback,
+                      const ProgressCallback& progress_callback);
+  virtual ~DownloadFileRequest();
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadFileRequest);
+};
 
 }  // namespace drive
 }  // namespace google_apis