Move download extension api implementation to download/ dir.

chrome/browser/download/download_extension_api_constants.cc

Index: chrome/browser/download/download_extension_api_constants.cc
diff --git a/chrome/browser/extensions/extension_downloads_api_constants.cc b/chrome/browser/download/download_extension_api_constants.cc
similarity index 92%
rename from chrome/browser/extensions/extension_downloads_api_constants.cc
rename to chrome/browser/download/download_extension_api_constants.cc
index 4a0db5307bb1329e215eadb19fd9e19c58c3d87c..aaf783b2e58e52844c0f30efe84d9ac7c994500a 100644
--- a/chrome/browser/extensions/extension_downloads_api_constants.cc
+++ b/chrome/browser/download/download_extension_api_constants.cc
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/extensions/extension_downloads_api_constants.h"
+#include "chrome/browser/download/download_extension_api_constants.h"
 
-namespace extension_downloads_api_constants {
+namespace download_extension_api_constants {
 
 // Error messages
 const char kNotImplemented[] = "NotImplemented";
@@ -62,4 +62,5 @@ const char* StateString(DownloadItem::DownloadState state) {
       return "";
   }
 }
-}  // namespace extension_downloads_api_constants
+
+}  // namespace download_extension_api_constants