GN: Don't depend on dart_bootstrap if there is a usable prebuilt sdk

utils/compiler/BUILD.gn

Index: utils/compiler/BUILD.gn
diff --git a/utils/compiler/BUILD.gn b/utils/compiler/BUILD.gn
index e13cea230584352ed964d9a67750d71068946f63..c0e428db69c192bd4cd9ab28836b550dc4fa5b3e 100644
--- a/utils/compiler/BUILD.gn
+++ b/utils/compiler/BUILD.gn
@@ -2,8 +2,9 @@
 # for details. 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/compiled_action.gni")
 import("../create_timestamp.gni")
-import("../invoke_dart.gni")
+import("../application_snapshot.gni")
 
 create_timestamp_file("dart2js_files_stamp") {
   path = rebase_path("../../pkg/compiler/lib")
@@ -20,7 +21,8 @@ create_timestamp_file("dartdoc_files_stamp") {
   output = "$target_gen_dir/dartdoc_files.stamp"
 }
 
-invoke_dart("dart2js_create_snapshot_entries") {
+compiled_action("dart2js_create_snapshot_entries") {
+  tool = "../../runtime/bin:dart"
   deps = [
     ":dart2js_files_stamp",
     ":dartdoc_files_stamp",