Allow multiple dart <script> tags in .sky files

sky/tests/modules/dart-imports-loader-interaction.sky

Index: sky/tests/modules/dart-imports-loader-interaction.sky
diff --git a/sky/tests/modules/dart-imports-loader-interaction.sky b/sky/tests/modules/dart-imports-loader-interaction.sky
new file mode 100644
index 0000000000000000000000000000000000000000..cbcdcee3ed6bf30fe870be4f38a6c30181678ee6
--- /dev/null
+++ b/sky/tests/modules/dart-imports-loader-interaction.sky
@@ -0,0 +1,12 @@
+<import src='resources/with-dart-import.sky' as='test'></import>
+<script>
+import "dart:sky.internals" as internals;
+
+void main() {
+    // The HTMLImportsLoader used to think with-dart-import load completed
+    // and did not know about with-dart-import having dart import statements
+    // which had made the load/execution of the script asynchronous.
+    String result = test.didInit ? "PASS" : "FAIL";
+    internals.notifyTestComplete(result);
+}
+</script>