Dart: Rebase generated imports from the SDK to the SDK base directory.

mojo/services/http_server/public/interfaces/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/module_args/mojo.gni")
 import("$mojo_sdk_root/mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
     "http_request.mojom",
     "http_response.mojom",
     "http_server.mojom",
     "http_server_factory.mojom",
   ]
 
   import_dirs = [ get_path_info("../../../", "abspath") ]
 
   if (defined(mojo_network_service_root)) {
     import_dirs += [ mojo_network_service_root ]
   } else {
     mojo_network_service_root = "../../.."
   }
 
   deps = [
     "$mojo_network_service_root/network/public/interfaces",
   ]
+
+  import_from = mojo_root
 }