Move 'dart:mojo.internal' into sdk_ext directory of mojo package

sky/engine/bindings/BUILD.gn

 # Copyright 2015 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("//sky/engine/bindings/bindings.gni")
 import("//sky/engine/core/core.gni")
 
 source_set("bindings") {
   sources = [
     "builtin.cc",
@@ skipping 43 matching lines @@
 }
 
 action("generate_snapshot_bin") {
   deps = [
     "//dart/runtime/bin:gen_snapshot($host_toolchain)",
     ":generate_dart_sky",
   ]
   inputs = [
     "//dart/runtime/tools/create_snapshot_bin.py",
     "//sky/engine/bindings/builtin.dart",
-    "//mojo/public/dart/lib/internal.dart",
-    "//mojo/public/dart/lib/src/handle_watcher.dart",
-    "//mojo/public/dart/lib/src/natives.dart",
-    "//mojo/public/dart/lib/src/timer_queue.dart",
+    "//mojo/public/dart/sdk_ext/internal.dart",
+    "//mojo/public/dart/sdk_ext/src/handle_watcher.dart",
+    "//mojo/public/dart/sdk_ext/src/natives.dart",
+    "//mojo/public/dart/sdk_ext/src/timer_queue.dart",
     "snapshot.dart",
   ]
   vm_isolate_snapshot = "$target_gen_dir/vm_isolate_snapshot.bin"
   isolate_snapshot = "$target_gen_dir/isolate_snapshot.bin"
   outputs = [
     vm_isolate_snapshot,
     isolate_snapshot,
   ]
 
   builtin_path = rebase_path("//sky/engine/bindings/builtin.dart")
   dart_sky_path = rebase_path("$bindings_output_dir/dart_sky.dart")
-  internal_path = rebase_path("//mojo/public/dart/lib/internal.dart")
+  internal_path = rebase_path("//mojo/public/dart/sdk_ext/internal.dart")
 
   gen_snapshot_dir =
       get_label_info("//dart/runtime/bin:gen_snapshot($host_toolchain)",
                      "root_out_dir")
   script = "//dart/runtime/tools/create_snapshot_bin.py"
 
   args = [
     "--executable",
     rebase_path("$gen_snapshot_dir/gen_snapshot"),
     "--package_root",
@@ skipping 305 matching lines @@
   ]
 
   include_dirs = [
     "..",
     "$root_build_dir",
   ]
 
   sources = get_target_outputs(":compile_idls")
   sources += get_target_outputs(":generate_dart_globals")
 }