Implement diff algorithm for libraries.

dart/sdk/lib/_internal/compiler/implementation/library_loader.dart

 // Copyright (c) 2012, 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.library_loader;
 
 import 'dart:async';
 import 'dart2jslib.dart'
     show Compiler,
          CompilerTask,
@@ skipping 480 matching lines @@
     // TODO(johnniwinther): Create erroneous library elements for missing
     // libraries.
     Uri readableUri =
         compiler.translateResolvedUri(importingLibrary, resolvedUri, node);
     if (readableUri == null) return new Future.value();
     LibraryElement library = libraryCanonicalUriMap[resolvedUri];
     if (library != null) {
       return new Future.value(library);
     }
     return compiler.withCurrentElement(importingLibrary, () {
-      return compiler.readScript(node, readableUri)
-          .then((Script script) {
-            if (script == null) return null;
-            LibraryElement element = new LibraryElementX(script, resolvedUri);
-            compiler.withCurrentElement(element, () {
-              handler.registerNewLibrary(element);
-              native.maybeEnableNative(compiler, element);
-              libraryCanonicalUriMap[resolvedUri] = element;
-              compiler.scanner.scanLibrary(element);
-            });
-            return processLibraryTags(handler, element).then((_) {
-              compiler.withCurrentElement(element, () {
-                handler.registerLibraryExports(element);
-              });
-              return element;
-            });
+      return compiler.readScript(node, readableUri).then((Script script) {
+        if (script == null) return null;
+        LibraryElement element =
+            createLibrarySync(handler, script, resolvedUri);
+        return processLibraryTags(handler, element).then((_) {
+          compiler.withCurrentElement(element, () {
+            handler.registerLibraryExports(element);
           });
+          return element;
+        });
+      });
+    });
+  }
+
+  LibraryElement createLibrarySync(
+      LibraryDependencyHandler handler,
+      Script script,
+      Uri resolvedUri) {
+    LibraryElement element = new LibraryElementX(script, resolvedUri);
+    return compiler.withCurrentElement(element, () {
+      if (handler != null) {
+        handler.registerNewLibrary(element);
+        libraryCanonicalUriMap[resolvedUri] = element;
+      }
+      native.maybeEnableNative(compiler, element);
+      compiler.scanner.scanLibrary(element);
+      return element;
     });
   }
 }
 
 
 /**
  * The fields of this class models a state machine for checking script
  * tags come in the correct order.
  */
 class TagState {
@@ skipping 427 matching lines @@
    * fixed-point computation of the import/export scopes.
    */
   void registerLibraryExports(LibraryElement library) {
     nodeMap[library].registerInitialExports();
   }
 
   Future processLibraryTags(LibraryElement library) {
     return task.processLibraryTags(this, library);
   }
 }