Refactoring DownloadManager::DownloadURL to add proper annotation.

Refactoring DownloadManager::DownloadURL to add proper network traffic
annotation. All changed files have received a NO_TRAFFIC_ANNOTATION_YET
tag instead of proper annotation and will be annotated in next CLs.

BUG=656607
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2860593003
Cr-Commit-Position: refs/heads/master@{#476312}
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index ed882eff..626c4c8 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -127,6 +127,7 @@
 #include "net/base/url_util.h"
 #include "net/http/http_cache.h"
 #include "net/http/http_transaction_factory.h"
+#include "net/traffic_annotation/network_traffic_annotation.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "ppapi/features/features.h"
@@ -3209,7 +3210,7 @@
     }
   }
   BrowserContext::GetDownloadManager(GetBrowserContext())
-      ->DownloadUrl(std::move(params));
+      ->DownloadUrl(std::move(params), NO_TRAFFIC_ANNOTATION_YET);
 }
 
 void WebContentsImpl::GenerateMHTML(