Update dart2js diagnostics to prepare for filtering.

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

Index: sdk/lib/_internal/compiler/implementation/library_loader.dart
diff --git a/sdk/lib/_internal/compiler/implementation/library_loader.dart b/sdk/lib/_internal/compiler/implementation/library_loader.dart
index 478f36fd6b18cf7995415ad227bee41662d771a8..53e79da8940d381ad77b39269501451fcaa8b85b 100644
--- a/sdk/lib/_internal/compiler/implementation/library_loader.dart
+++ b/sdk/lib/_internal/compiler/implementation/library_loader.dart
@@ -343,16 +343,16 @@ class LibraryLoaderTask extends LibraryLoader {
       LibraryElement existing =
           libraryNames.putIfAbsent(name, () => library);
       if (!identical(existing, library)) {
-        Uri uri = library.entryCompilationUnit.script.uri;
-        compiler.reportMessage(
-            compiler.spanFromSpannable(tag.name, uri),
-            MessageKind.DUPLICATED_LIBRARY_NAME.error({'libraryName': name}),
-            api.Diagnostic.WARNING);
-        Uri existingUri = existing.entryCompilationUnit.script.uri;
-        compiler.reportMessage(
-            compiler.spanFromSpannable(existing.libraryTag.name, existingUri),
-            MessageKind.DUPLICATED_LIBRARY_NAME.error({'libraryName': name}),
-            api.Diagnostic.WARNING);
+        compiler.withCurrentElement(library, () {
+          compiler.reportWarning(tag.name,
+              MessageKind.DUPLICATED_LIBRARY_NAME,
+              {'libraryName': name});
+        });
+        compiler.withCurrentElement(existing, () {
+          compiler.reportWarning(existing.libraryTag.name,
+              MessageKind.DUPLICATED_LIBRARY_NAME,
+              {'libraryName': name});
+        });
       }
     }
   }