allow JS builtin to be typed as needed

lib/runtime/dart/_js_helper.js

 dart_library.library('dart/_js_helper', null, /* Imports */[
   'dart/_runtime',
   'dart/core',
   'dart/collection',
   'dart/_interceptors',
   'dart/_foreign_helper'
 ], /* Lazy imports */[
 ], function(exports, dart, core, collection, _interceptors, _foreign_helper) {
   'use strict';
   let dartx = dart.dartx;
@@ skipping 101 matching lines @@
         } catch (e) {
           return e;
         }
 
       })();
       if (regexp instanceof RegExp) return regexp;
       let errorMessage = String(regexp);
       dart.throw(new core.FormatException(`Illegal RegExp pattern: ${source}, ${errorMessage}`));
     }
     firstMatch(string) {
-      let m = dart.as(this[_nativeRegExp].exec(checkString(string)), core.List$(core.String));
+      let m = this[_nativeRegExp].exec(checkString(string));
       if (m == null) return null;
       return new _MatchImplementation(this, m);
     }
     hasMatch(string) {
       return this[_nativeRegExp].test(checkString(string));
     }
     stringMatch(string) {
       let match = this.firstMatch(string);
       if (match != null) return match.group(0);
       return null;
     }
     allMatches(string, start) {
       if (start === void 0) start = 0;
       checkString(string);
       checkInt(start);
       if (dart.notNull(start) < 0 || dart.notNull(start) > dart.notNull(string[dartx.length])) {
         dart.throw(new core.RangeError.range(start, 0, string[dartx.length]));
       }
       return new _AllMatchesIterable(this, string, start);
     }
     [_execGlobal](string, start) {
       let regexp = this[_nativeGlobalVersion];
       regexp.lastIndex = start;
-      let match = dart.as(regexp.exec(string), core.List);
+      let match = regexp.exec(string);
       if (match == null) return null;
       return new _MatchImplementation(this, dart.as(match, core.List$(core.String)));
     }
     [_execAnchored](string, start) {
       let regexp = this[_nativeAnchoredVersion];
       regexp.lastIndex = start;
-      let match = dart.as(regexp.exec(string), core.List);
+      let match = regexp.exec(string);
       if (match == null) return null;
       if (match[dartx.get](dart.notNull(match[dartx.length]) - 1) != null) return null;
       match[dartx.length] = dart.notNull(match[dartx.length]) - 1;
       return new _MatchImplementation(this, dart.as(match, core.List$(core.String)));
     }
     matchAsPrefix(string, start) {
       if (start === void 0) start = 0;
       if (dart.notNull(start) < 0 || dart.notNull(start) > dart.notNull(string[dartx.length])) {
         dart.throw(new core.RangeError.range(start, 0, string[dartx.length]));
       }
@@ skipping 325 matching lines @@
       checkNull(from);
       dart.throw("String.replace(Pattern) UNIMPLEMENTED");
     }
   }
   dart.fn(stringReplaceFirstUnchecked, dart.dynamic, [dart.dynamic, dart.dynamic, dart.dynamic], [core.int]);
   function stringJoinUnchecked(array, separator) {
     return array.join(separator);
   }
   dart.fn(stringJoinUnchecked);
   function getRuntimeType(object) {
-    return dart.as(dart.realRuntimeType(object), core.Type);
+    return dart.realRuntimeType(object);
   }
   dart.fn(getRuntimeType, core.Type, [dart.dynamic]);
   function getIndex(array, index) {
     dart.assert(isJsArray(array));
     return array[index];
   }
   dart.fn(getIndex, dart.dynamic, [dart.dynamic, core.int]);
   function getLength(array) {
     dart.assert(isJsArray(array));
     return array.length;
@@ skipping 11 matching lines @@
     constructors: () => ({_Patch: [_Patch, []]})
   });
   const patch = dart.const(new _Patch());
   class InternalMap extends core.Object {}
   class Primitives extends core.Object {
     static initializeStatics(id) {
       Primitives.mirrorFunctionCacheName = dart.notNull(Primitives.mirrorFunctionCacheName) + `_${id}`;
       Primitives.mirrorInvokeCacheName = dart.notNull(Primitives.mirrorInvokeCacheName) + `_${id}`;
     }
     static objectHashCode(object) {
-      let hash = dart.as(object.$identityHash, core.int);
+      let hash = object.$identityHash;
       if (hash == null) {
         hash = Math.random() * 0x3fffffff | 0;
         object.$identityHash = hash;
       }
       return hash;
     }
     static _throwFormatException(string) {
       dart.throw(new core.FormatException(string));
     }
     static parseInt(source, radix, handleError) {
@@ skipping 148 matching lines @@
       dart.throw(new core.RangeError.range(dart.as(charCode, core.num), 0, 1114111));
     }
     static stringConcatUnchecked(string1, string2) {
       return _foreign_helper.JS_STRING_CONCAT(string1, string2);
     }
     static flattenString(str) {
       return str.charCodeAt(0) == 0 ? str : str;
     }
     static getTimeZoneName(receiver) {
       let d = Primitives.lazyAsJsDate(receiver);
-      let match = dart.as(/\((.*)\)/.exec(d.toString()), core.List);
+      let match = /\((.*)\)/.exec(d.toString());
       if (match != null) return dart.as(match[dartx.get](1), core.String);
-      match = dart.as(/^[A-Z,a-z]{3}\s[A-Z,a-z]{3}\s\d+\s\d{2}:\d{2}:\d{2}\s([A-Z]{3,5})\s\d{4}$/.exec(d.toString()), core.List);
+      match = /^[A-Z,a-z]{3}\s[A-Z,a-z]{3}\s\d+\s\d{2}:\d{2}:\d{2}\s([A-Z]{3,5})\s\d{4}$/.exec(d.toString());
       if (match != null) return dart.as(match[dartx.get](1), core.String);
-      match = dart.as(/(?:GMT|UTC)[+-]\d{4}/.exec(d.toString()), core.List);
+      match = /(?:GMT|UTC)[+-]\d{4}/.exec(d.toString());
       if (match != null) return dart.as(match[dartx.get](0), core.String);
       return "";
     }
     static getTimeZoneOffsetInMinutes(receiver) {
       return -Primitives.lazyAsJsDate(receiver).getTimezoneOffset();
     }
     static valueFromDecomposedDate(years, month, day, hours, minutes, seconds, milliseconds, isUtc) {
       let MAX_MILLISECONDS_SINCE_EPOCH = 8640000000000000;
       checkInt(years);
       checkInt(month);
@@ skipping 227 matching lines @@
   const _trace = Symbol('_trace');
   class _StackTrace extends core.Object {
     _StackTrace(exception) {
       this[_exception] = exception;
       this[_trace] = null;
     }
     toString() {
       if (this[_trace] != null) return this[_trace];
       let trace = null;
       if (typeof this[_exception] === "object") {
-        trace = dart.as(this[_exception].stack, core.String);
+        trace = this[_exception].stack;
       }
       return this[_trace] = trace == null ? '' : trace;
     }
   }
   _StackTrace[dart.implements] = () => [core.StackTrace];
   dart.setSignature(_StackTrace, {
     constructors: () => ({_StackTrace: [_StackTrace, [dart.dynamic]]})
   });
   function objectHashCode(object) {
     if (object == null || typeof object != 'object') {
@@ skipping 131 matching lines @@
     class SyncIterator extends core.Object {
       SyncIterator(jsIterator) {
         this[_jsIterator] = jsIterator;
         this[_current] = null;
       }
       get current() {
         return this[_current];
       }
       moveNext() {
         let ret = this[_jsIterator].next();
-        this[_current] = dart.as(ret.value, E);
+        this[_current] = ret.value;
         return !ret.done;
       }
     }
     SyncIterator[dart.implements] = () => [core.Iterator$(E)];
     dart.setSignature(SyncIterator, {
       constructors: () => ({SyncIterator: [SyncIterator$(E), [dart.dynamic]]}),
       methods: () => ({moveNext: [core.bool, []]})
     });
     return SyncIterator;
   });
@@ skipping 78 matching lines @@
   exports.CastErrorImplementation = CastErrorImplementation;
   exports.FallThroughErrorImplementation = FallThroughErrorImplementation;
   exports.RuntimeError = RuntimeError;
   exports.random64 = random64;
   exports.jsonEncodeNative = jsonEncodeNative;
   exports.SyncIterator$ = SyncIterator$;
   exports.SyncIterator = SyncIterator;
   exports.SyncIterable$ = SyncIterable$;
   exports.SyncIterable = SyncIterable;
 });