Only add JS once, and not to very single patched library.

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.
  */
 final bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 361 matching lines @@
 
     //patchDartLibrary(coreLibrary, 'core');
     //patchDartLibrary(coreImplLibrary, 'coreimpl');
   }
 
   void patchDartLibrary(LibraryElement library, String dartLibraryPath) {
     if (library.isPatched) return;
     Uri patchUri = resolvePatchUri(dartLibraryPath);
     if (patchUri !== null) {
        patchParser.patchLibrary(patchUri, library);
-      // We allow foreign functions in patched libraries.
-      addForeignFunctions(library);  // Is safe even if already added.
       // TODO(lrn): Make this lazy.
       applyClassPatches(library);
     }
   }
 
   void applyClassPatches(LibraryElement library) {
     for (Element element in library.localMembers) {
       if (element.isClass()) {
         ClassElement classElement = element;
         if (classElement.isPatched) {
@@ skipping 541 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)';
 }