Allow multiple dart <script> tags in .sky files

sky/tests/modules/multiple-scripts-import.sky

Index: sky/tests/modules/multiple-scripts-import.sky
diff --git a/sky/tests/modules/multiple-scripts-import.sky b/sky/tests/modules/multiple-scripts-import.sky
new file mode 100644
index 0000000000000000000000000000000000000000..8d32e7579f7108dd1b97c83998f5dd0f0f3dd8da
--- /dev/null
+++ b/sky/tests/modules/multiple-scripts-import.sky
@@ -0,0 +1,19 @@
+<sky>
+<import src='resources/multiple-scripts-child.sky' as='child'></import>
+<script>
+import "../resources/third_party/unittest/unittest.dart";
+import "../resources/unit.dart";
+
+import "dart:sky";
+import "dart:sky.internals";
+
+void main () {
+  initUnit();
+
+  test('multiple libraries should combine using "as"', () {
+    expect(child.one, 'one');
+    expect(child.two, 'two');
+  });
+}
+</script>
+</sky>