First take on support of library private names.

lib/compiler/implementation/dart_backend/renamer.dart

Index: lib/compiler/implementation/dart_backend/renamer.dart
diff --git a/lib/compiler/implementation/dart_backend/renamer.dart b/lib/compiler/implementation/dart_backend/renamer.dart
index bc49a1a185871ed6609746deb7b4f97c61059329..f0a44032969ccdf1f43f78bf97bff0a513e8cd08 100644
--- a/lib/compiler/implementation/dart_backend/renamer.dart
+++ b/lib/compiler/implementation/dart_backend/renamer.dart
@@ -10,12 +10,33 @@ class SendRenamer extends ResolvedVisitor<String> {
   String visitSuperSend(Send node) => null;
   String visitOperatorSend(Send node) => null;
   String visitClosureSend(Send node) => null;
-  String visitDynamicSend(Send node) => null;
   String visitForeignSend(Send node) => null;
 
+  String tryRenamePrivateId(Send node) {
+    Identifier selector = node.selector.asIdentifier();
+    assert(selector !== null);
+    String originalName = selector.source.slowToString();
+    if (originalName.startsWith('_')) {
+      String newName = renamer.renamePrivateId(
+          renamer.context.getLibrary(), originalName);
+      if (node.receiver !== null) {
+        // TODO: ugly, should be fixed with new renamer infrastructure.
+        String receiver = new Unparser(renamer).unparse(node.receiver);
+        newName = '$receiver.$newName';
+      }
+      return newName;
+    }
+
+    return null;
+  }
+
+  String visitDynamicSend(Send node) => tryRenamePrivateId(node);
+
   String visitGetterSend(Send node) {
     final element = elements[node];
-    if (element === null || !element.isTopLevel()) return null;
+    if (element === null || !element.isTopLevel()) {
+      return tryRenamePrivateId(node);
+    }
     return renamer.renameElement(element);
   }
 
@@ -67,6 +88,7 @@ class ConflictingRenamer extends Renamer {
   final Map<LibraryElement, Map<String, String>> renamed;
   final Set<String> usedTopLevelIdentifiers;
   final Map<LibraryElement, String> imports;
+  int privateNameCounter = 0;
   TreeElements contextElements;
   Element context;
 
@@ -121,13 +143,34 @@ class ConflictingRenamer extends Renamer {
         return renameElement(enclosingClass);
       }
     }
-    if (context.isFunction() && context.cachedNode.name == node) {
+    if (context.isFunction() && context.isTopLevel() &&
+        context.cachedNode.name == node) {
       return renameElement(context);
     }
+    // TODO: as the rest of renameIdentifier should go closer to
+    // Emitter.outputElement.
+    // Note: this code should only rename private identifiers for class'
+    // fields/getters/setters/methods.  Top-level identifiers are renamed
+    // just to escape conflicts and that should be enough as we shouldn't
+    // be able to resolve private identifiers for other libraries.
+    final originalName = node.source.slowToString();
+    if (originalName.startsWith('_')) {
+      return '${renamePrivateId(context.getLibrary(), originalName)}';
+    }
     return null;
   }
 
+  String getName(LibraryElement library, String originalName, renamer) =>
+      renamed.putIfAbsent(library, () => <String>{})
+          .putIfAbsent(originalName, renamer);
+
+  String renamePrivateId(LibraryElement library, String originalName) =>
+      getName(library, originalName,
+              () => '_${privateNameCounter++}${originalName}');
+
   String renameElement(Element element) {
+    assert(element.isTopLevel());
+
     // This comes from currently buggy TypeAnnotation renamer.
     // It should be solved in there and it will be solved with
     // new fancy renamer. TODO: remove this cruft.
@@ -136,18 +179,13 @@ class ConflictingRenamer extends Renamer {
     // TODO(smok): Make sure that the new name does not conflict with existing
     // local identifiers.
     generateUniqueName(name) {
-      while (usedTopLevelIdentifiers.contains(name)) {
-        name = "p_$name";
-      }
+      while (usedTopLevelIdentifiers.contains(name)) name = 'p_$name';
       usedTopLevelIdentifiers.add(name);
       return name;
     }
 
     String originalName = element.name.slowToString();
-
-    // TODO(antonm): we should rename lib private names as well.
-    if (!element.isTopLevel()) return originalName;
-    final library = element.getLibrary();
+    LibraryElement library = element.getLibrary();
     if (library === compiler.coreLibrary) return originalName;
     if (isDartCoreLib(compiler, library)) {
       final prefix =
@@ -155,7 +193,7 @@ class ConflictingRenamer extends Renamer {
       return '$prefix.$originalName';
     }
 
-    return renamed.putIfAbsent(library, () => <String>{})
-        .putIfAbsent(originalName, () => generateUniqueName(originalName));
+    return getName(library, originalName,
+                   () => generateUniqueName(originalName));
   }
 }