[fasta] Flip source flag and include source by default

pkg/front_end/lib/src/fasta/source/source_loader.dart

Index: pkg/front_end/lib/src/fasta/source/source_loader.dart
diff --git a/pkg/front_end/lib/src/fasta/source/source_loader.dart b/pkg/front_end/lib/src/fasta/source/source_loader.dart
index 3c67c0cdc7668f6d4e23f360ac07fe28dd38faee..7c4d8781d5d30527f2c0483dc4d8563d082a5d00 100644
--- a/pkg/front_end/lib/src/fasta/source/source_loader.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_loader.dart
@@ -46,7 +46,7 @@ import '../compiler_context.dart' show CompilerContext;
 
 class SourceLoader<L> extends Loader<L> {
   final Map<Uri, List<int>> sourceBytes = <Uri, List<int>>{};
-  final includeSource = CompilerContext.current.options.includeSource;
+  final excludeSource = CompilerContext.current.options.excludeSource;
 
   // Used when building directly to kernel.
   ClassHierarchy hierarchy;
@@ -92,7 +92,7 @@ class SourceLoader<L> extends Loader<L> {
   }
 
   List<int> getSource(List<int> bytes) {
-    if (!includeSource) return const <int>[];
+    if (excludeSource) return const <int>[];
 
     // bytes is 0-terminated. We don't want that included.
     if (bytes is Uint8List) {