Start propagating non-primitive types in the backend, and fold instructions that know about the typ…

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
===================================================================
--- lib/compiler/implementation/compiler.dart	(revision 6727)
+++ lib/compiler/implementation/compiler.dart	(working copy)
@@ -385,6 +385,10 @@
     enqueuer.registerInvocation(methodName, selector);
   }
 
+  void registerDynamicInvocationOf(Element element) {
+    addToWorkList(element);
+  }
+
   void registerDynamicGetter(SourceString methodName) {
     enqueuer.registerGetter(methodName);
   }