Refactor the way we emit no such method handlers so it's easier to optimize it later.

lib/compiler/implementation/namer.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class Namer {
   final Compiler compiler;
 
   static Set<String> _jsReserved = null;
   Set<String> get jsReserved() {
     if (_jsReserved === null) {
       _jsReserved = new Set<String>();
       _jsReserved.addAll(JsNames.javaScriptKeywords);
       _jsReserved.addAll(JsNames.reservedPropertySymbols);
     }
     return _jsReserved;
   }
 
   Map<Element, String> globals;
   Map<String, int> usedGlobals;
+  Map<String, Set<LibraryElement>> usedPrivateNames;
   Map<String, LibraryElement> shortPrivateNameOwners;
 
   Namer(this.compiler)
       : globals = new Map<Element, String>(),
         usedGlobals = new Map<String, int>(),
+        usedPrivateNames = new Map<String, Set<LibraryElement>>(),
         shortPrivateNameOwners = new Map<String, LibraryElement>();
 
   final String CURRENT_ISOLATE = @'$';
   final String ISOLATE = 'Isolate';
   final String ISOLATE_PROPERTIES = @"$isolateProperties";
   /** Some closures must contain their name. The name is stored in
     * [STATIC_CLOSURE_NAME_NAME]. */
   final String STATIC_CLOSURE_NAME_NAME = @'$name';
   final SourceString CLOSURE_INVOCATION_NAME = const SourceString(@'$call');
 
@@ skipping 33 matching lines @@
       parts[i] = parts[j];
       parts[j] = tmp;
     }
     return safeName(Strings.join(parts, "_"));
   }
 
   String privateName(LibraryElement lib, SourceString name) {
     if (name.isPrivate()) {
       String nameString = name.slowToString();
 
+      // TODO(kasperl): This is a bit of a hacky way of keeping track
+      // of the libraries that use a particular private name.
+      Set<LibraryElement> usedBy =
+          usedPrivateNames.putIfAbsent(nameString, () =>
+                                       new Set<LibraryElement>());
+      usedBy.add(lib);
+
       // The first library asking for a short private name wins.
       LibraryElement owner =
           shortPrivateNameOwners.putIfAbsent(nameString, () => lib);
       // If a private name could clash with a mangled private name we don't
       // use the short name. For example a private name "_lib3_foo" would
       // clash with "_foo" from "lib3".
       if (owner === lib && !nameString.startsWith('_$LIBRARY_PREFIX')) {
         return nameString;
       }
       String libName = getName(lib);
@@ skipping 178 matching lines @@
   }
 
   String safeName(String name) {
     if (jsReserved.contains(name) || name.startsWith('\$')) {
       name = "\$$name";
       assert(!jsReserved.contains(name));
     }
     return name;
   }
 }