dart2js: fix dependency tracking for deferred loading when types are only used

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index 3213f9f52dfbaad0b5fd6e5ee88e0e7c20b1916d..e261ff6d8f6fe51df293d7fbe5f2f41524584439 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -280,6 +280,23 @@ class DeferredLoadTask extends CompilerTask {
 
         elements.add(dependency);
       }
+
+      void registerTypeArgumentsAsDependencies(DartType type) {
+        Element dependency = type.element;
+        if (dependency == null || dependency.isErroneous ||
+            dependency.isTypeVariable) {
+          return;
+        }
+        elements.add(dependency);
+        if (type is GenericType) {
+          type.typeArguments.forEach(registerTypeArgumentsAsDependencies);
+        }
+      }
+
+      treeElements.forEachType((Node node, DartType type) {
+        if (node is NewExpression) registerTypeArgumentsAsDependencies(type);
+      });
+
       treeElements.forEachConstantNode((Node node, _) {
         // Explicitly depend on the backend constants.
         ConstantValue value =