Change assert implementation to not depend on a top-level function called 'assert'.

lib/compiler/implementation/compiler.dart

 // Copyright (c) 2012, 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.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 const bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 345 matching lines @@
     coreImplLibrary = scanBuiltinLibrary('coreimpl');
     jsHelperLibrary = scanBuiltinLibrary('_js_helper');
     interceptorsLibrary = scanBuiltinLibrary('_interceptors');
 
     addForeignFunctions(jsHelperLibrary);
     addForeignFunctions(interceptorsLibrary);
 
     libraries['dart:core'] = coreLibrary;
     libraries['dart:coreimpl'] = coreImplLibrary;
 
-    assertMethod = coreLibrary.find(const SourceString('assert'));
+    assertMethod = jsHelperLibrary.find(const SourceString('assert'));
 
     initializeSpecialClasses();
   }
 
   void importCoreLibrary(LibraryElement library) {
     Uri coreUri = new Uri.fromComponents(scheme: 'dart', path: 'core');
     if (coreLibrary === null) {
       coreLibrary = scanner.loadLibrary(coreUri, null, coreUri);
     }
     scanner.importLibrary(library,
@@ skipping 549 matching lines @@
     final endOffset = end.charOffset + end.slowCharCount;
 
     // [begin] and [end] might be the same for the same empty token. This
     // happens for instance when scanning '$$'.
     assert(endOffset >= beginOffset);
     return f(beginOffset, endOffset);
   }
 
   String toString() => 'SourceSpan($uri, $begin, $end)';
 }