Load deferred chunks in the right order.

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart

Index: sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
index 3418c9aec9fca13e7b506b5afbd867dc790794e0..57bd6038bf3d9d3a5dfd82c444086229af00db13 100644
--- a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
@@ -1439,17 +1439,22 @@ mainBuffer.add(r'''
       // [emitOneShotInterceptors] have been called.
       emitCompileTimeConstants(mainBuffer, mainOutputUnit);
 
-      // We write a javascript mapping from DeferredLibrary elements
-      // (really their String argument) to the js hunk to load.
+      // Write a javascript mapping from Deferred import load ids (derrived from
+      // the import prefix.) to a list of lists of js hunks to load.
       // TODO(sigurdm): Create a syntax tree for this.
       // TODO(sigurdm): Also find out where to place it.
       mainBuffer.write("\$.libraries_to_load = {");
-      for (String constant in compiler.deferredLoadTask.hunksToLoad.keys) {
+      for (String loadId in compiler.deferredLoadTask.hunksToLoad.keys) {
         // TODO(sigurdm): Escape these strings.
-        mainBuffer.write('"$constant":[');
-        for (OutputUnit outputUnit in
-            compiler.deferredLoadTask.hunksToLoad[constant]) {
-          mainBuffer.write('"${outputUnit.partFileName(compiler)}.part.js", ');
+        mainBuffer.write('"$loadId":[');
+        for (List<OutputUnit> outputUnits in
+            compiler.deferredLoadTask.hunksToLoad[loadId]) {
+          mainBuffer.write("[");
+          for (OutputUnit outputUnit in outputUnits) {
+            mainBuffer
+              .write('"${outputUnit.partFileName(compiler)}.part.js", ');
+          }
+          mainBuffer.write("],");
         }
         mainBuffer.write("],\n");
       }