Introduce "platform configurations" to replace categories and libraries.dart.

pkg/compiler/lib/src/dart_backend/backend.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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 337 matching lines @@
     }
   }
 
   @override
   bool enableDeferredLoadingIfSupported(Spannable node, Registry registry) {
     // TODO(sigurdm): Implement deferred loading for dart2dart.
     reporter.reportWarningMessage(
         node, MessageKind.DEFERRED_LIBRARY_DART_2_DART);
     return false;
   }
+
+  @override
+  Uri resolvePatchUri(String libraryName, Uri) {
+    // Dart2dart does not use patches.
+    return null;
+  }
 }
 
 class DartImpactTransformer extends ImpactTransformer {
   final DartBackend backend;
 
   DartImpactTransformer(this.backend);
 
   @override
   WorldImpact transformResolutionImpact(ResolutionImpact worldImpact) {
     TransformedWorldImpact transformed =
@@ skipping 190 matching lines @@
   }
 
   // TODO(johnniwinther): Remove this when values are computed from the
   // expressions.
   @override
   void copyConstantValues(DartConstantTask task) {
     constantCompiler.constantValueMap.addAll(
         task.constantCompiler.constantValueMap);
   }
 }