Revert of Revert of Drive: Let DriveUploader use batch request API.

google_apis/drive/drive_api_requests.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "google_apis/drive/drive_api_requests.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/json/json_writer.h"
 #include "base/location.h"
@@ skipping 1193 matching lines @@
     child->request->RunCallbackOnPrematureFailure(result);
     sender_->RequestFinished(child->request);
     child_requests_.erase(child);
   }
   MayCompletePrepare();
 }
 
 void BatchUploadRequest::Commit() {
   DCHECK(CalledOnValidThread());
   DCHECK(!committed_);
-  CHECK(!child_requests_.empty());
-  committed_ = true;
-  MayCompletePrepare();
+  if (child_requests_.empty()) {
+    Cancel();
+  } else {
+    committed_ = true;
+    MayCompletePrepare();
+  }
 }
 
 void BatchUploadRequest::Prepare(const PrepareCallback& callback) {
   DCHECK(CalledOnValidThread());
   DCHECK(!callback.is_null());
   prepare_callback_ = callback;
   MayCompletePrepare();
 }
 
 void BatchUploadRequest::Cancel() {
@@ skipping 117 matching lines @@
 void BatchUploadRequest::RunCallbackOnPrematureFailure(DriveApiErrorCode code) {
   for (auto child : child_requests_) {
     child.request->RunCallbackOnPrematureFailure(code);
     sender_->RequestFinished(child.request);
   }
   child_requests_.clear();
 }
 
 }  // namespace drive
 }  // namespace google_apis