add checks needed for covariant generics, and List<E>

lib/runtime/dart/_js_helper.js

 var _js_helper;
 (function(exports) {
   'use strict';
   class NoSideEffects extends core.Object {
     NoSideEffects() {
     }
   }
   class NoThrows extends core.Object {
     NoThrows() {
     }
@@ skipping 23 matching lines @@
       get isNotEmpty() {
         return !dart.notNull(this.isEmpty);
       }
       toString() {
         return collection.Maps.mapToString(this);
       }
       [_throwUnmodifiable]() {
         throw new core.UnsupportedError("Cannot modify unmodifiable Map");
       }
       set(key, val) {
+        dart.as(key, K);
+        dart.as(val, V);
         return this[_throwUnmodifiable]();
       }
       putIfAbsent(key, ifAbsent) {
+        dart.as(key, K);
+        dart.as(ifAbsent, dart.functionType(V, []));
         return dart.as(this[_throwUnmodifiable](), V);
       }
       remove(key) {
+        dart.as(key, K);
         return dart.as(this[_throwUnmodifiable](), V);
       }
       clear() {
         return this[_throwUnmodifiable]();
       }
       addAll(other) {
         return this[_throwUnmodifiable]();
       }
     }
     ConstantMap[dart.implements] = () => [core.Map$(K, V)];
     dart.defineNamedConstructor(ConstantMap, '_');
     return ConstantMap;
   });
   let ConstantMap = ConstantMap$();
   let _jsObject = Symbol('_jsObject');
   let _keys = Symbol('_keys');
   let _fetch = Symbol('_fetch');
   let ConstantStringMap$ = dart.generic(function(K, V) {
     class ConstantStringMap extends ConstantMap$(K, V) {
       _(length, jsObject, keys) {
         this.length = length;
         this[_jsObject] = jsObject;
         this[_keys] = keys;
         super._();
       }
       containsValue(needle) {
+        dart.as(needle, V);
         return this.values[core.$any](value => dart.equals(value, needle));
       }
       containsKey(key) {
         if (!(typeof key == 'string'))
           return false;
         if (dart.equals('__proto__', key))
           return false;
         return jsHasOwnProperty(this[_jsObject], dart.as(key, core.String));
       }
       get(key) {
@@ skipping 20 matching lines @@
     }
     ConstantStringMap[dart.implements] = () => [_internal.EfficientLength];
     dart.defineNamedConstructor(ConstantStringMap, '_');
     return ConstantStringMap;
   });
   let ConstantStringMap = ConstantStringMap$();
   let _protoValue = Symbol('_protoValue');
   let ConstantProtoMap$ = dart.generic(function(K, V) {
     class ConstantProtoMap extends ConstantStringMap$(K, V) {
       _(length, jsObject, keys, protoValue) {
+        dart.as(protoValue, V);
         this[_protoValue] = protoValue;
         super._(dart.as(length, core.int), jsObject, dart.as(keys, core.List$(K)));
       }
       containsKey(key) {
         if (!(typeof key == 'string'))
           return false;
         if (dart.equals('__proto__', key))
           return true;
         return jsHasOwnProperty(this[_jsObject], dart.as(key, core.String));
       }
@@ skipping 31 matching lines @@
         super._();
       }
       [_getMap]() {
         if (!this.$map) {
           let backingMap = new (collection.LinkedHashMap$(K, V))();
           this.$map = fillLiteralMap(this[_jsData], backingMap);
         }
         return this.$map;
       }
       containsValue(needle) {
+        dart.as(needle, V);
         return this[_getMap]().containsValue(needle);
       }
       containsKey(key) {
         return this[_getMap]().containsKey(key);
       }
       get(key) {
         return this[_getMap]().get(key);
       }
       forEach(f) {
         this[_getMap]().forEach(f);
@@ skipping 3886 matching lines @@
   exports.jsonEncodeNative = jsonEncodeNative;
   exports.getIsolateAffinityTag = getIsolateAffinityTag;
   exports.LoadLibraryFunctionType = LoadLibraryFunctionType;
   exports.DeferredLoadCallback = DeferredLoadCallback;
   exports.loadDeferredLibrary = loadDeferredLibrary;
   exports.MainError = MainError;
   exports.missingMain = missingMain;
   exports.badMain = badMain;
   exports.mainHasTooManyParameters = mainHasTooManyParameters;
 })(_js_helper || (_js_helper = {}));