Land Alexander's change that throw on abstract class instantiations.

lib/compiler/implementation/lib/js_helper.dart

Index: lib/compiler/implementation/lib/js_helper.dart
diff --git a/lib/compiler/implementation/lib/js_helper.dart b/lib/compiler/implementation/lib/js_helper.dart
index 07c28ae63d56f5486f177f63d34a6c33b91959d2..2515116cb2341911efe17ec713a3cc5406feb7ce 100644
--- a/lib/compiler/implementation/lib/js_helper.dart
+++ b/lib/compiler/implementation/lib/js_helper.dart
@@ -849,6 +849,10 @@ throwRuntimeError(message) {
   throw new RuntimeError(message);
 }
 
+throwAbstractClassInstantiationError(className) {
+  throw new AbstractClassInstantiationError(className);
+}
+
 /**
  * Called from catch blocks in generated code to extract the Dart
  * exception from the thrown value. The thrown value may have been