Fix a couple codegen crashers

test/codegen/expect/cascade.js

 var cascade;
 (function(exports) {
   'use strict';
   class A extends core.Object {
     A() {
       this.x = null;
     }
   }
   // Function test_closure_with_mutate: () → void
   function test_closure_with_mutate() {
@@ skipping 55 matching lines @@
   // Function test_VariableDeclaration_first: () → void
   function test_VariableDeclaration_first() {
     let a = (() => {
       let _ = new core.List.from([]);
       _[core.$length] = 2;
       _[core.$add](3);
       return _;
     })(), b = 2;
     core.print(a);
   }
+  // Function test_increment: () → void
+  function test_increment() {
+    let a = new A();
+    let y = ((() => {
+      a.x = dart.dbinary(a.x, '+', 1);
+      a.x = dart.dbinary(a.x, '-', 1);
+      return a;
+    })());
+  }
   let Base$ = dart.generic(function(T) {
     class Base extends core.Object {
       Base() {
         this.x = new core.List$(T).from([]);
       }
     }
     return Base;
   });
   let Base = Base$();
   class Foo extends Base$(core.int) {
     test_final_field_generic(t) {
       this.x[core.$add](1);
       this.x[core.$add](2);
       this.x[core.$add](3);
       this.x[core.$add](4);
     }
   }
   // Exports:
   exports.A = A;
   exports.test_closure_with_mutate = test_closure_with_mutate;
   exports.test_closure_without_mutate = test_closure_without_mutate;
   exports.test_mutate_inside_cascade = test_mutate_inside_cascade;
   exports.test_mutate_outside_cascade = test_mutate_outside_cascade;
   exports.test_VariableDeclaration_single = test_VariableDeclaration_single;
   exports.test_VariableDeclaration_last = test_VariableDeclaration_last;
   exports.test_VariableDeclaration_first = test_VariableDeclaration_first;
+  exports.test_increment = test_increment;
   exports.Base$ = Base$;
   exports.Base = Base;
   exports.Foo = Foo;
 })(cascade || (cascade = {}));