Read SDK and patches from a JSON file.

pkg/front_end/lib/src/fasta/loader.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.loader;
 
 import 'dart:async' show Future;
 
 import 'dart:collection' show Queue;
 
@@ skipping 25 matching lines @@
   Loader(this.target);
 
   Ticker get ticker => target.ticker;
 
   /// Look up a library builder by the name [uri], or if such doesn't
   /// exist, create one. The canonical URI of the library is [uri], and its
   /// actual location is [fileUri].
   ///
   /// Canonical URIs have schemes like "dart", or "package", and the actual
   /// location is often a file URI.
-  LibraryBuilder read(Uri uri, [Uri fileUri]) {
+  LibraryBuilder read(Uri uri, {Uri fileUri, bool isPatch: false}) {
     firstSourceUri ??= uri;
     LibraryBuilder builder = builders.putIfAbsent(uri, () {
       if (fileUri == null) {
         switch (uri.scheme) {
           case "package":
           case "dart":
             fileUri = target.translateUri(uri);
             break;
 
           default:
             fileUri = uri;
             break;
         }
       }
-      LibraryBuilder library = target.createLibraryBuilder(uri, fileUri);
+      LibraryBuilder library =
+          target.createLibraryBuilder(uri, fileUri, isPatch);
       if (uri.scheme == "dart" && uri.path == "core") {
         coreLibrary = library;
         target.loadExtraRequiredLibraries(this);
       }
+      if (uri.scheme == "dart") {
+        target.readPatchFiles(library);
+      }
       first ??= library;
       if (library.loader == this) {
         unparsedLibraries.addLast(library);
       }
       return library;
     });
     return builder;
   }
 
   void ensureCoreLibrary() {
@@ skipping 65 matching lines @@
   Builder getNativeAnnotation() => target.getNativeAnnotation(this);
 
   Builder getAbstractClassInstantiationError() {
     return target.getAbstractClassInstantiationError(this);
   }
 }
 
 String format(double d, int fractionDigits, int width) {
   return d.toStringAsFixed(fractionDigits).padLeft(width);
 }