Read SDK and patches from a JSON file.

pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
index 12a9d7a0afa48a060936ddd1540b92f623a98aab..a0b818dc8b347e8292d87643e0e6450417ea4019 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
@@ -61,6 +61,8 @@ class KernelLibraryBuilder
     extends SourceLibraryBuilder<KernelTypeBuilder, Library> {
   final Library library;
 
+  final bool isPatch;
+
   final Map<String, SourceClassBuilder> mixinApplicationClasses =
       <String, SourceClassBuilder>{};
 
@@ -71,7 +73,7 @@ class KernelLibraryBuilder
   final List<KernelTypeVariableBuilder> boundlessTypeVariables =
       <KernelTypeVariableBuilder>[];
 
-  KernelLibraryBuilder(Uri uri, Uri fileUri, Loader loader)
+  KernelLibraryBuilder(Uri uri, Uri fileUri, Loader loader, this.isPatch)
       : library = new Library(uri, fileUri: relativizeUri(fileUri)),
         super(loader, fileUri);