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 31 matching lines @@
   /// actual location is [fileUri].
   ///
   /// Canonical URIs have schemes like "dart", or "package", and the actual
   /// location is often a file URI.
   ///
   /// The [accessor] is the library that's trying to import, export, or include
   /// as part [uri], and [charOffset] is the location of the corresponding
   /// directive. If [accessor] isn't allowed to access [uri], it's a
   /// compile-time error.
   LibraryBuilder read(Uri uri, int charOffset,
-      {Uri fileUri, LibraryBuilder accessor}) {
+      {Uri fileUri, LibraryBuilder accessor, 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;
     });
     // TODO(ahe): Check that [accessor] is allowed to access [builder].
     return builder;
   }
 
@@ skipping 66 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);
 }