Start including sdk_ext sources in sky dart-pkg

mojo/public/dart/rules.gni

Index: mojo/public/dart/rules.gni
diff --git a/mojo/public/dart/rules.gni b/mojo/public/dart/rules.gni
index f3a2481d086fd4133c57960610f0badf07a1ae5f..628c43edb9db069829d0309e6a3533b90d1e0ef5 100644
--- a/mojo/public/dart/rules.gni
+++ b/mojo/public/dart/rules.gni
@@ -220,6 +220,9 @@ template("dartzip_packaged_application") {
 #
 #   datadeps (optional)
 #
+#   sdk_ext_directory (optional)
+#       Directory containing sdk-ext .dart sources.
+#
 template("dart_pkg") {
   pubspec_yaml_path = rebase_path("pubspec.yaml")
   dart_package_name_script =
@@ -263,6 +266,11 @@ template("dart_pkg") {
                                    "list lines")
     }
 
+    sdk_ext_directory = []
+    if (defined(invoker.sdk_ext_directory)) {
+      sdk_ext_directory += [ invoker.sdk_ext_directory ]
+    }
+
     script = rebase_path("mojo/public/tools/dart_pkg.py", ".", mojo_sdk_root)
     outputs = [
       stamp_file,
@@ -271,7 +279,7 @@ template("dart_pkg") {
     inputs = [
                list_mojoms_script,
                script,
-             ] + rebase_path(invoker.sources)
+             ] + rebase_path(invoker.sources) + rebase_path(sdk_ext_directory)
 
     args = [
              "--package-name",
@@ -286,6 +294,7 @@ template("dart_pkg") {
              rebase_path(stamp_file),
              "--package-sources",
            ] + rebase_path(invoker.sources) + [ "--mojom-sources" ] +
-           rebase_path(mojom_sources, "", mojo_sdk_root)
+           rebase_path(mojom_sources, "", mojo_sdk_root) +
+           [ "--sdk-ext-directories" ] + rebase_path(sdk_ext_directory)
   }
 }