Add option for outputting a deferred loading mapping.

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index f11b6545e07036c08ab9558dca600908930a6545..2b0ab4d236b111b289753f172816dabc20c23abf 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -40,6 +40,7 @@ import 'elements/elements.dart' show
 
 import 'util/util.dart' show
     Link, makeUnique;
+import 'util/uri_extras.dart' as uri_extras;
 
 import 'util/setlet.dart' show
     Setlet;
@@ -146,6 +147,10 @@ class DeferredLoadTask extends CompilerTask {
   final Map<Import, LibraryElement> _allDeferredImports =
       new Map<Import, LibraryElement>();
 
+  /// Because the token-stream is forgotten later in the program, we cache a
+  /// description of each deferred import.
+  final _deferredImportDescriptions = new Map<Import, ImportDescription>();
+
   // For each deferred import we want to know exactly what elements have to
   // be loaded.
   Map<Import, Set<Element>> _importedDeferredBy = null;
@@ -617,7 +622,7 @@ class DeferredLoadTask extends CompilerTask {
     });
   }
 
-  void ensureMetadataResolved(Compiler compiler) {
+  void beforeResolution(Compiler compiler) {
     if (compiler.mainApp == null) return;
     _allDeferredImports[_fakeMainImport] = compiler.mainApp;
     var lastDeferred;
@@ -671,7 +676,10 @@ class DeferredLoadTask extends CompilerTask {
           // The last import we saw with the same prefix.
           Import previousDeferredImport = prefixDeferredImport[prefix];
           if (import.isDeferred) {
-            _allDeferredImports[import] = library.getLibraryFromTag(import);
+            LibraryElement importedLibrary = library.getLibraryFromTag(import);
+            _allDeferredImports[import] = importedLibrary;
+            _deferredImportDescriptions[import] =
+                new ImportDescription(import, library, compiler);
 
             if (prefix == null) {
               compiler.reportError(import,
@@ -764,4 +772,37 @@ class DeferredLoadTask extends CompilerTask {
     }
     return null;
   }
+
+  /// Returns a json-style map for describing what files that are loaded by a
+  /// given deferred import.
+  Map deferredMap() {

[floitsch, 2015/01/05 14:10:38]

has a getter name.
Either make it a getter, or change the name.

[sigurdm, 2015/01/05 15:23:08]

Done.

+    JavaScriptBackend backend = compiler.backend;
+    Map mapping = {};
+    _deferredImportDescriptions.keys.forEach((ast.Import import) {
+      List<OutputUnit> outputUnits = hunksToLoad[importDeferName[import]];
+      ImportDescription description = _deferredImportDescriptions[import];
+      Map a = mapping.putIfAbsent(description.importingUri, () => {});

[floitsch, 2015/01/05 14:10:38]

what's "a" ?
Type the map (both static and dynamic).

[sigurdm, 2015/01/05 15:23:08]

Fixed the name.
Done.

+
+      a[description.prefix] = outputUnits.map(
+          (OutputUnit outputUnit) {
+        return backend.emitter.oldEmitter.deferredPartFileName(outputUnit);

[floitsch, 2015/01/05 14:10:38]

Don't go through "oldEmitter".
The best is probably currently to add a "emitter.deferredPartFileName" to the
emitter task. That said, it could be shared code. (Currently it is duplicated by
copy/paste).

[sigurdm, 2015/01/05 15:23:08]

Moved it to backend.

+      }).toList();
+    });
+    return mapping;
+  }
 }
+
+class ImportDescription {
+  /// Relative uri to the importing library.
+  final String importingUri;
+  /// The prefix this import is imported as.
+  final String prefix;
+
+  ImportDescription(Import import,
+                    LibraryElement importingLibrary,
+                    Compiler compiler)
+      : importingUri = uri_extras.relativize(
+          compiler.mainApp.canonicalUri,
+          importingLibrary.canonicalUri, false),
+        prefix = import.prefix.source;
+}