Support imports for dart: libs.

lib/compiler/implementation/dart_backend/renamer.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.
 
 /**
  * Renames only top-level elements that would let to ambiguity if not renamed.
  * TODO(smok): Make sure that top-level fields are correctly renamed.
  */
 class ConflictingRenamer extends Renamer {
   final Compiler compiler;
   final Map<Element, String> renamed;
   final Set<String> usedTopLevelIdentifiers;
+  final Map<LibraryElement, String> imports;
   TreeElements contextElements;
   Element context;
 
   Map<Element, TreeElements> get resolvedElements() =>
       compiler.enqueuer.resolution.resolvedElements;
 
   ConflictingRenamer(this.compiler) :
       renamed = new Map<Element, String>(),
-      usedTopLevelIdentifiers = new Set<String>();
+      usedTopLevelIdentifiers = new Set<String>(),
+      imports = new Map<LibraryElement, String>();
 
   void setContext(Element element) {
     this.context = element;
     contextElements = resolvedElements[element];
   }
 
   String getFactoryName(FunctionExpression node) =>
       node.name.asSend().selector.asIdentifier().source.slowToString();
 
   bool isNamedConstructor(Element element) =>
@@ skipping 43 matching lines @@
         return renameElement(enclosingClass);
       }
     }
     if (context.isFunction() && context.cachedNode.name == node) {
       return renameElement(context);
     }
     return null;
   }
 
   String renameElement(Element element) {
+    generateUniqueName(name) {
+      while (usedTopLevelIdentifiers.contains(name)) {
+        name = "x$name";
+      }
+      usedTopLevelIdentifiers.add(name);
+      return name;
+    }
+
     String originalName = element.name.slowToString();
-    if (element.getLibrary() == compiler.coreLibrary || !element.isTopLevel()) {
-      return originalName;
+    // TODO(antonm): we should rename lib private names as well.
+    if (!element.isTopLevel()) return originalName;
+    final library = element.getLibrary();
+    if (library === compiler.coreLibrary) return originalName;
+    if (isDartCoreLib(compiler, library)) {
+      final prefix = imports.putIfAbsent(library, () => generateUniqueName('p'));
+      return '$prefix.$originalName';
     }
     if (renamed[element] !== null) {
       return renamed[element];
     }
 
     // Not renamed and top element.
     // TODO(smok): Make sure that the new name does not conflict with existing
     // local identifiers.
-    String name = originalName;
-    while (usedTopLevelIdentifiers.contains(name)) {
-      name = "_$name";
-    }
-    usedTopLevelIdentifiers.add(name);
-    renamed[element] = name;
-    return name;
+    return renamed[element] = generateUniqueName(originalName);
   }
 }