Read SDK and patches from a JSON file.

pkg/front_end/lib/src/fasta/target_implementation.dart

 // Copyright (c) 2016, 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 fasta.target_implementation;
 
 import 'package:kernel/target/targets.dart' as backend show Target;
 
 import 'builder/builder.dart' show Builder, ClassBuilder, LibraryBuilder;
 
@@ skipping 19 matching lines @@
 
   Builder cachedCompileTimeError;
   Builder cachedAbstractClassInstantiationError;
   Builder cachedNativeAnnotation;
 
   TargetImplementation(Ticker ticker, this.uriTranslator, this.backendTarget)
       : super(ticker);
 
   /// Creates a [LibraryBuilder] corresponding to [uri], if one doesn't exist
   /// already.
-  LibraryBuilder createLibraryBuilder(Uri uri, Uri fileUri);
+  LibraryBuilder createLibraryBuilder(Uri uri, Uri fileUri, bool isPatch);
 
   /// Add the classes extended or implemented directly by [cls] to [set].
   void addDirectSupertype(ClassBuilder cls, Set<ClassBuilder> set);
 
   /// Returns all classes that will be included in the resulting program.
   List<ClassBuilder> collectAllClasses();
 
   /// The class [cls] is involved in a cyclic definition. This method should
   /// ensure that the cycle is broken, for example, by removing superclass and
   /// implemented interfaces.
@@ skipping 37 matching lines @@
     }
   }
 
   Token skipNativeClause(Token token) => vm.skipNativeClause(token);
 
   String extractNativeMethodName(Token token) =>
       unescapeString(token.next.lexeme);
 
   void addSourceInformation(
       Uri uri, List<int> lineStarts, List<int> sourceCode);
+
+  void readPatchFiles(LibraryBuilder library) {
+    assert(library.uri.scheme == "dart");
+    List<Uri> patches = uriTranslator.patches[library.uri.path];
+    if (patches != null) {
+      for (Uri patch in patches) {
+        library.loader.read(patch, -1, fileUri: patch, isPatch: true);
+      }
+    }
+  }
 }