Initialize the deferred global for every fragment.

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.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.
 
 library dart2js.js_emitter.startup_emitter.model_emitter;
 
 import 'dart:convert' show JsonEncoder;
 
 import 'package:js_runtime/shared/embedded_names.dart' show
     CLASS_FIELDS_EXTRACTOR,
@@ skipping 190 matching lines @@
     Map<DeferredFragment, String> hunkHashes =
         writeDeferredFragments(deferredFragmentsCode);
 
     // Now that we have written the deferred hunks, we can update the hash
     // tokens in the main-fragment.
     deferredHashTokens.forEach((DeferredFragment key,
                                 _DeferredFragmentHash token) {
       token.setHash(hunkHashes[key]);
     });
 
-    writeMainFragment(mainFragment, mainCode);
+    writeMainFragment(mainFragment, mainCode,
+      isSplit: program.deferredFragments.isNotEmpty);
 
     if (backend.requiresPreamble &&
         !backend.htmlLibraryIsLoaded) {
       reporter.reportHintMessage(
           NO_LOCATION_SPANNABLE, MessageKind.PREAMBLE);
     }
 
     if (compiler.deferredMapUri != null) {
       writeDeferredMap();
     }
@@ skipping 20 matching lines @@
       Map<DeferredFragment, js.Expression> fragmentsCode) {
     Map<DeferredFragment, String> hunkHashes = <DeferredFragment, String>{};
 
     fragmentsCode.forEach((DeferredFragment fragment, js.Expression code) {
       hunkHashes[fragment] = writeDeferredFragment(fragment, code);
     });
 
     return hunkHashes;
   }
 
+  js.Statement buildDeferredInitializerGlobal() {
+    String global = deferredInitializersGlobal;
+    return js.js.statement(
+        "if (typeof($global) === 'undefined') var # = Object.create(null);",
+        new js.VariableDeclaration(global, allowRename: false));
+  }
+
   // Writes the given [fragment]'s [code] into a file.
   //
   // Updates the shared [outputBuffers] field with the output.
-  void writeMainFragment(MainFragment fragment, js.Statement code) {
+  void writeMainFragment(MainFragment fragment, js.Statement code,
+      {bool isSplit}) {
     LineColumnCollector lineColumnCollector;
     List<CodeOutputListener> codeOutputListeners;
     if (shouldGenerateSourceMap) {
       lineColumnCollector = new LineColumnCollector();
       codeOutputListeners = <CodeOutputListener>[lineColumnCollector];
     }
 
     CodeOutput mainOutput = new StreamCodeOutput(
             compiler.outputProvider('', 'js'),
             codeOutputListeners);
     outputBuffers[fragment] = mainOutput;
 
     js.Program program = new js.Program([
         buildGeneratedBy(),
         new js.Comment(HOOKS_API_USAGE),
+        isSplit ? buildDeferredInitializerGlobal() : new js.Block.empty(),
         code]);
 
     mainOutput.addBuffer(js.prettyPrint(program, compiler,
         monitor: compiler.dumpInfoTask));
 
     if (shouldGenerateSourceMap) {
       mainOutput.add(
           generateSourceMapTag(compiler.sourceMapUri, compiler.outputUri));
     }
 
@@ skipping 33 matching lines @@
     // hunk is loaded.
     // That function must be in a map from its hashcode to the function. Since
     // we don't know the hash before we actually emit the code we store the
     // function in a temporary field first:
     //
     //   deferredInitializer.current = <pretty-printed code>;
     //   deferredInitializer[<hash>] = deferredInitializer.current;
 
     js.Program program = new js.Program([
         buildGeneratedBy(),
+        buildDeferredInitializerGlobal(),
         js.js.statement('$deferredInitializersGlobal.current = #', code)]);
 
     output.addBuffer(js.prettyPrint(program, compiler,
         monitor: compiler.dumpInfoTask));
 
     // Make a unique hash of the code (before the sourcemaps are added)
     // This will be used to retrieve the initializing function from the global
     // variable.
     String hash = hasher.getHash();
 
@@ skipping 69 matching lines @@
     // Json does not support comments, so we embed the explanation in the
     // data.
     mapping["_comment"] = "This mapping shows which compiled `.js` files are "
         "needed for a given deferred library import.";
     mapping.addAll(compiler.deferredLoadTask.computeDeferredMap());
     compiler.outputProvider(compiler.deferredMapUri.path, 'deferred_map')
       ..add(const JsonEncoder.withIndent("  ").convert(mapping))
       ..close();
   }
 }