Better boolean conversion tests.

tool/input_sdk/private/ddc_runtime/operations.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This library defines runtime operations on objects used by the code
 /// generator.
 part of dart._runtime;
 
 _canonicalFieldName(obj, name, args, displayName) => JS('', '''(() => {
   $name = $canonicalMember($obj, $name);
@@ skipping 243 matching lines @@
 @JSExportName('as')
 cast(obj, type) {
   if (obj == null) return obj;
 
   bool result = strongInstanceOf(obj, type, true);
   if (JS('bool', '#', result)) return obj;
   _throwCastError(obj, type, result);
 }
 
 bool test(obj) {
-  if (JS('bool', 'typeof # == "boolean"', obj)) return JS('bool', '#', obj);
-  throwCastError(getReifiedType(obj), JS('', '#', bool));
+  if (obj is bool) return obj;
+  return booleanConversionFailed(obj);
+}
+
+bool booleanConversionFailed(obj) {
+  if (obj == null) {
+    throw new BooleanConversionAssertionError();
+  }
+  var actual = getReifiedType(obj);
+  var expected = JS('', '#', bool);
+  throw new TypeErrorImplementation.fromMessage(
+      "type '${typeName(actual)}' is not a subtype of "
+      "type '${typeName(expected)}' in boolean expression");
 }
 
 void _throwCastError(obj, type, bool result) {
   var actual = getReifiedType(obj);
   if (result == false) throwCastError(actual, type);
 
   throwStrongModeError('Strong mode cast failure from ' +
       typeName(actual) + ' to ' + typeName(type));
 }
 
@@ skipping 240 matching lines @@
     constructor(dartIterator) {
       this.dartIterator = dartIterator;
     }
     next() {
       let i = this.dartIterator;
       let done = !i.moveNext();
       return { done: done, value: done ? void 0 : i.current };
     }
   }
 ''');