fasta: Cache source bytes to ensure we use the same bytes for outline and bodies, Gives also around…

pkg/front_end/lib/src/fasta/source/source_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.source_loader;
 
 import 'dart:async' show
     Future;
 
 import 'dart:io' show
@@ skipping 53 matching lines @@
 import 'diet_parser.dart' show
     DietParser;
 
 import 'source_library_builder.dart' show
     SourceLibraryBuilder;
 
 import '../ast_kind.dart' show
     AstKind;
 
 class SourceLoader<L> extends Loader<L> {
+  final Map<Uri, List<int>> sourceBytes = <Uri, List<int>>{};
+
   // Used when building directly to kernel.
   ClassHierarchy hierarchy;
   CoreTypes coreTypes;
 
   // Used when building analyzer ASTs.
   ElementStore elementStore;
 
   SourceLoader(TargetImplementation target)
       : super(target);
 
   Future<Token> tokenize(SourceLibraryBuilder library,
       {bool suppressLexicalErrors: false}) async {
     Uri uri = library.fileUri;
     if (uri == null || uri.scheme != "file") {
       return inputError(library.uri, -1, "Not found: ${library.uri}.");
     }
     try {
-      List<int> bytes = await readBytesFromFile(uri);
+      List<int> bytes = sourceBytes[uri];
+      if (bytes == null) {
+        bytes = sourceBytes[uri] = await readBytesFromFile(uri);
+      }
       byteCount += bytes.length - 1;
       ScannerResult result = scan(bytes);
       Token token = result.tokens;
       if (!suppressLexicalErrors) {
         target.addLineStarts(library.fileUri, result.lineStarts);
       }
       while (token is ErrorToken) {
         if (!suppressLexicalErrors) {
           ErrorToken error = token;
           print(new InputError(uri, token.charOffset, error.assertionMessage)
@@ skipping 262 matching lines @@
     ticker.logMs("Built analyzer element model.");
   }
 
   void computeHierarchy(Program program) {
     hierarchy = new ClassHierarchy(program);
     ticker.logMs("Computed class hierarchy");
     coreTypes = new CoreTypes(program);
     ticker.logMs("Computed core types");
   }
 }