Fix Flutter Dart role

sdk/lib/rules.gni

Index: sdk/lib/rules.gni
diff --git a/sdk/lib/rules.gni b/sdk/lib/rules.gni
index 93ade221871799e2642368200853891a869bf6a3..0aa80f87006278ef5d0e36325686390cda860cd2 100644
--- a/sdk/lib/rules.gni
+++ b/sdk/lib/rules.gni
@@ -9,10 +9,13 @@
 #       The name of a Dart SDK library.
 #
 # Optional arguments:
+#   destination
+#       Base path to copy sources. Default value is "$root_gen_dir/dart_sdk".
+#
 #   dart_root
 #       Path to the Dart SDK source root. Default value is "//dart".
 #
-# The sources will be copied into $root_gen_dir/dart_sdk_libs/$sdk_lib_name/.
+# The sources will be copied into $root_gen_dir/dart_sdk/$sdk_lib_name/.
 #
 template("dart_sdk_lib_copy") {
   assert(defined(invoker.sdk_lib_name))
@@ -21,6 +24,11 @@ template("dart_sdk_lib_copy") {
   } else {
     dart_root = rebase_path("//dart")
   }
+  if (defined(invoker.destination)) {
+    destination = invoker.destination
+  } else {
+    destination = "$root_gen_dir/dart_sdk"
+  }
   dart_sdk_sdk_lib_path =
       rebase_path("sdk/lib", "", dart_root)
   dart_sdk_tools_gypi_to_gn_path =
@@ -39,6 +47,6 @@ template("dart_sdk_lib_copy") {
                   [rebase_path(lib_sources_gypi, "", lib_path)])
   copy(target_name) {
     sources = rebase_path(sdk_lib_sources_gypi.sources, "", lib_path)
-    outputs = [ "$root_gen_dir/dart_sdk_libs/$lib_name/{{source_file_part}}" ]
+    outputs = [ "$destination/$lib_name/{{source_file_part}}" ]
   }
 }