Typecheck constructor initializers properly

test/codegen/expect/collection/collection.js

 var collection;
 (function(collection) {
   'use strict';
   let _HashMap$ = dart.generic(function(K, V) {
     class _HashMap extends dart.Object {
       _HashMap() {
         this._length = 0;
         this._strings = null;
         this._nums = null;
         this._rest = null;
@@ skipping 269 matching lines @@
       }
     }
     return _IdentityHashMap;
   });
   let _IdentityHashMap = _IdentityHashMap$(dynamic, dynamic);
   let _CustomHashMap$ = dart.generic(function(K, V) {
     class _CustomHashMap extends _HashMap$(K, V) {
       _CustomHashMap(_equals, _hashCode, validKey) {
         this._equals = _equals;
         this._hashCode = _hashCode;
-        this._validKey = validKey !== null ? validKey : (v) => dart.is(v, K);
+        this._validKey = dart.as(validKey !== null ? validKey : (v) => dart.is(v, K), _Predicate);
         super._HashMap();
       }
       get(key) {
         if (!dart.notNull(this._validKey(key)))
           return dart.as(null, V);
         return super._get(key);
       }
       set(key, value) {
         super._set(key, value);
       }
@@ skipping 372 matching lines @@
       }
     }
     return _LinkedIdentityHashMap;
   });
   let _LinkedIdentityHashMap = _LinkedIdentityHashMap$(dynamic, dynamic);
   let _LinkedCustomHashMap$ = dart.generic(function(K, V) {
     class _LinkedCustomHashMap extends _LinkedHashMap$(K, V) {
       _LinkedCustomHashMap(_equals, _hashCode, validKey) {
         this._equals = _equals;
         this._hashCode = _hashCode;
-        this._validKey = validKey !== null ? validKey : (v) => dart.is(v, K);
+        this._validKey = dart.as(validKey !== null ? validKey : (v) => dart.is(v, K), _Predicate);
         super._LinkedHashMap();
       }
       get(key) {
         if (!dart.notNull(this._validKey(key)))
           return dart.as(null, V);
         return super._get(key);
       }
       set(key, value) {
         super._set(key, value);
       }
@@ skipping 344 matching lines @@
       }
     }
     return _IdentityHashSet;
   });
   let _IdentityHashSet = _IdentityHashSet$(dynamic);
   let _CustomHashSet$ = dart.generic(function(E) {
     class _CustomHashSet extends _HashSet$(E) {
       _CustomHashSet(_equality, _hasher, validKey) {
         this._equality = _equality;
         this._hasher = _hasher;
-        this._validKey = validKey !== null ? validKey : (x) => dart.is(x, E);
+        this._validKey = dart.as(validKey !== null ? validKey : (x) => dart.is(x, E), _Predicate);
         super._HashSet();
       }
       _newSet() {
         return new _CustomHashSet(this._equality, this._hasher, this._validKey);
       }
       _findBucketIndex(bucket, element) {
         if (bucket === null)
           return -1;
         let length = dart.as(dart.dinvokef(/* Unimplemented unknown name */JS, 'int', '#.length', bucket), core.int);
         for (let i = 0; i < length; i++) {
@@ skipping 347 matching lines @@
       }
     }
     return _LinkedIdentityHashSet;
   });
   let _LinkedIdentityHashSet = _LinkedIdentityHashSet$(dynamic);
   let _LinkedCustomHashSet$ = dart.generic(function(E) {
     class _LinkedCustomHashSet extends _LinkedHashSet$(E) {
       _LinkedCustomHashSet(_equality, _hasher, validKey) {
         this._equality = _equality;
         this._hasher = _hasher;
-        this._validKey = validKey !== null ? validKey : (x) => dart.is(x, E);
+        this._validKey = dart.as(validKey !== null ? validKey : (x) => dart.is(x, E), _Predicate);
         super._LinkedHashSet();
       }
       _newSet() {
         return new _LinkedCustomHashSet(this._equality, this._hasher, this._validKey);
       }
       _findBucketIndex(bucket, element) {
         if (bucket === null)
           return -1;
         let length = dart.as(dart.dinvokef(/* Unimplemented unknown name */JS, 'int', '#.length', bucket), core.int);
         for (let i = 0; i < length; i++) {
@@ skipping 2782 matching lines @@
     return _TypeTest;
   });
   let _TypeTest = _TypeTest$(dynamic);
   let SplayTreeMap$ = dart.generic(function(K, V) {
     class SplayTreeMap extends _SplayTree$(K) {
       SplayTreeMap(compare, isValidKey) {
         if (compare === void 0)
           compare = null;
         if (isValidKey === void 0)
           isValidKey = null;
-        this._comparator = compare === null ? core.Comparable.compare : compare;
-        this._validKey = isValidKey !== null ? isValidKey : (v) => dart.is(v, K);
+        this._comparator = dart.as(compare === null ? core.Comparable.compare : compare, core.Comparator);
+        this._validKey = dart.as(isValidKey !== null ? isValidKey : (v) => dart.is(v, K), _Predicate);
         super._SplayTree();
       }
       SplayTreeMap$from(other, compare, isValidKey) {
         if (compare === void 0)
           compare = null;
         if (isValidKey === void 0)
           isValidKey = null;
         let result = new SplayTreeMap();
         other.forEach((k, v) => {
           result.set(k, dart.as(v, V));
@@ skipping 338 matching lines @@
     return _SplayTreeNodeIterator;
   });
   let _SplayTreeNodeIterator = _SplayTreeNodeIterator$(dynamic);
   let SplayTreeSet$ = dart.generic(function(E) {
     class SplayTreeSet extends dart.mixin(_SplayTree$(E), IterableMixin$(E), SetMixin$(E)) {
       SplayTreeSet(compare, isValidKey) {
         if (compare === void 0)
           compare = null;
         if (isValidKey === void 0)
           isValidKey = null;
-        this._comparator = compare === null ? core.Comparable.compare : compare;
-        this._validKey = isValidKey !== null ? isValidKey : (v) => dart.is(v, E);
+        this._comparator = dart.as(compare === null ? core.Comparable.compare : compare, core.Comparator);
+        this._validKey = dart.as(isValidKey !== null ? isValidKey : (v) => dart.is(v, E), _Predicate);
         super._SplayTree();
       }
       SplayTreeSet$from(elements, compare, isValidKey) {
         if (compare === void 0)
           compare = null;
         if (isValidKey === void 0)
           isValidKey = null;
         let result = new SplayTreeSet(compare, isValidKey);
         for (let element of elements) {
           result.add(element);
@@ skipping 196 matching lines @@
   collection.ListQueue$ = ListQueue$;
   collection.SetMixin = SetMixin;
   collection.SetMixin$ = SetMixin$;
   collection.SetBase = SetBase;
   collection.SetBase$ = SetBase$;
   collection.SplayTreeMap = SplayTreeMap;
   collection.SplayTreeMap$ = SplayTreeMap$;
   collection.SplayTreeSet = SplayTreeSet;
   collection.SplayTreeSet$ = SplayTreeSet$;
 })(collection || (collection = {}));