Move file_handlers API from //chrome to //extensions

extensions/browser/api/file_handlers/BUILD.gn

Index: extensions/browser/api/file_handlers/BUILD.gn
diff --git a/extensions/browser/api/file_handlers/BUILD.gn b/extensions/browser/api/file_handlers/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..03b261ad532352f7848233e2581f744f993f963f
--- /dev/null
+++ b/extensions/browser/api/file_handlers/BUILD.gn
@@ -0,0 +1,14 @@
+# Copyright 2017 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.
+
+source_set("file_handlers") {
+  sources = [
+    "app_file_handler_util.cc",
+    "app_file_handler_util.h",
+    "directory_util.cc",
+    "directory_util.h",
+    "mime_util.cc",
+    "mime_util.h",
+  ]
+}