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

mojo/services/native_viewport/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 = [
     "native_viewport.mojom",
   ]
 
   import_dirs = [ get_path_info("../../../", "abspath") ]
 
   public_deps = [
     "../../../geometry/public/interfaces",
     "../../../gpu/public/interfaces",
     "../../../input_events/public/interfaces",
     "../../../surfaces/public/interfaces:surface_id",
   ]
+
+  import_from = mojo_root
 }