dart2js: Temporarily store output unit in Fragment.

pkg/compiler/lib/src/js_emitter/program_builder.dart

 // Copyright (c) 2014, 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.
 
 library dart2js.js_emitter.program_builder;
 
 import 'js_emitter.dart' show computeMixinClass;
 import 'model.dart';
 
 import '../common.dart';
@@ skipping 104 matching lines @@
       loadMap[loadId] = outputUnits
           .map((OutputUnit unit) => _outputs[unit])
           .toList(growable: false);
     });
     return loadMap;
   }
 
   MainFragment _buildMainOutput(LibrariesMap librariesMap) {
     // Construct the main output from the libraries and the registered holders.
     MainFragment result = new MainFragment(
+        librariesMap.outputUnit,
         "",  // The empty string is the name for the main output file.
         backend.emitter.staticFunctionAccess(_compiler.mainFunction),
         _buildLibraries(librariesMap),
         _buildStaticNonFinalFields(librariesMap),
         _buildStaticLazilyInitializedFields(librariesMap),
         _buildConstants(librariesMap),
         _registry.holders.toList(growable: false));
     _outputs[librariesMap.outputUnit] = result;
     return result;
   }
 
   DeferredFragment _buildDeferredOutput(MainFragment mainOutput,
                                       LibrariesMap librariesMap) {
     DeferredFragment result = new DeferredFragment(
+        librariesMap.outputUnit,
         backend.deferredPartFileName(librariesMap.name, addExtension: false),
                                      librariesMap.name,
         mainOutput,
         _buildLibraries(librariesMap),
         _buildStaticNonFinalFields(librariesMap),
         _buildStaticLazilyInitializedFields(librariesMap),
         _buildConstants(librariesMap));
     _outputs[librariesMap.outputUnit] = result;
     return result;
   }
@@ skipping 299 matching lines @@
       _registry.registerConstant(outputUnit, constantValue);
       assert(!_constants.containsKey(constantValue));
       String name = namer.constantName(constantValue);
       String constantObject = namer.globalObjectForConstant(constantValue);
       Holder holder = _registry.registerHolder(constantObject);
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     };
   }
 }