Re-apply "support for typedef in checked mode" and fix the checked mode failures on drt by not shar…

sdk/lib/_internal/compiler/implementation/ssa/codegen.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/codegen.dart	(revision 16252)
+++ sdk/lib/_internal/compiler/implementation/ssa/codegen.dart	(working copy)
@@ -2291,6 +2291,11 @@
     push(new js.Binary('==', pop(), new js.LiteralNull()));
   }
 
+  void checkNonNull(HInstruction input) {
+    use(input);
+    push(new js.Binary('!=', pop(), new js.LiteralNull()));
+  }
+
   void checkFunction(HInstruction input, DartType type) {
     checkTypeOf(input, '===', 'function');
     js.Expression functionTest = pop();
@@ -2415,6 +2420,12 @@
                || Elements.isListSupertype(element, compiler)) {
       handleListOrSupertypeCheck(input, type);
       attachLocationToLast(node);
+    } else if (element.isTypedef()) {
+      checkNonNull(input);
+      js.Expression nullTest = pop();
+      checkType(input, type);
+      push(new js.Binary('&&', nullTest, pop()));
+      attachLocationToLast(node);
     } else if (types[input].canBePrimitive() || types[input].canBeNull()) {
       checkObject(input, '===');
       js.Expression objectTest = pop();