Do not suppress implicit constructors that need a super call.

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 74 matching lines @@
   let Base$ = dart.generic(function(T) {
     class Base extends core.Object {
       Base() {
         this.x = dart.setType([], core.List$(T));
       }
     }
     return Base;
   });
   let Base = Base$();
   class Foo extends Base$(core.int) {
+    Foo() {
+      super.Base();
+    }
     test_final_field_generic(t) {
       this.x[core.$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 = {}));