Introduce ParallelDownloadJob.

content/browser/download/download_manager_impl.cc

Index: content/browser/download/download_manager_impl.cc
diff --git a/content/browser/download/download_manager_impl.cc b/content/browser/download/download_manager_impl.cc
index ccb9aaaf0deacd59c092df337c86b04ca8af2ba6..3a9f4287d12247c69ee5cd971fc9676a28e21ddb 100644
--- a/content/browser/download/download_manager_impl.cc
+++ b/content/browser/download/download_manager_impl.cc
@@ -519,16 +519,6 @@ void DownloadManagerImpl::AddUrlDownloader(
     url_downloaders_.push_back(std::move(downloader));
 }
 
-void DownloadManagerImpl::RemoveUrlDownloader(UrlDownloader* downloader) {
-  for (auto ptr = url_downloaders_.begin(); ptr != url_downloaders_.end();
-       ++ptr) {
-    if (ptr->get() == downloader) {
-      url_downloaders_.erase(ptr);
-      return;
-    }
-  }
-}
-
 // static
 DownloadInterruptReason DownloadManagerImpl::BeginDownloadRequest(
     std::unique_ptr<net::URLRequest> url_request,
@@ -714,6 +704,24 @@ DownloadItem* DownloadManagerImpl::GetDownloadByGuid(const std::string& guid) {
                                                      : nullptr;
 }
 
+void DownloadManagerImpl::OnUrlDownloaderStarted(
+    std::unique_ptr<DownloadCreateInfo> download_create_info,
+    std::unique_ptr<ByteStreamReader> stream_reader,
+    const DownloadUrlParameters::OnStartedCallback& callback) {
+  StartDownload(std::move(download_create_info), std::move(stream_reader),
+                callback);
+}
+
+void DownloadManagerImpl::OnUrlDownloaderStopped(UrlDownloader* downloader) {
+  for (auto ptr = url_downloaders_.begin(); ptr != url_downloaders_.end();
+       ++ptr) {
+    if (ptr->get() == downloader) {
+      url_downloaders_.erase(ptr);
+      return;
+    }
+  }
+}
+
 void DownloadManagerImpl::GetAllDownloads(DownloadVector* downloads) {
   for (const auto& it : downloads_) {
     downloads->push_back(it.second.get());