Clear StringToken.canonicalizer after each parsing.

pkg/analyzer/lib/src/dart/analysis/file_state.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.
 
 import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 16 matching lines @@
 import 'package:analyzer/src/summary/package_bundle_reader.dart';
 import 'package:analyzer/src/summary/summarize_ast.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
 import 'package:front_end/src/base/api_signature.dart';
 import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:front_end/src/fasta/builder/builder.dart' as fasta;
 import 'package:front_end/src/fasta/parser/parser.dart' as fasta;
 import 'package:front_end/src/fasta/scanner.dart' as fasta;
+import 'package:front_end/src/fasta/scanner/token.dart';
 import 'package:meta/meta.dart';
 
 /**
  * [FileContentOverlay] is used to temporary override content of files.
  */
 class FileContentOverlay {
   final _map = <String, String>{};
 
   /**
    * Return the paths currently being overridden.
@@ skipping 564 matching lines @@
       Token token = PerformanceStatistics.scan.makeCurrentWhile(() {
         return scanner.tokenize();
       });
       LineInfo lineInfo = new LineInfo(scanner.lineStarts);
 
       Parser parser = new Parser(source, errorListener);
       parser.enableAssertInitializer = analysisOptions.enableAssertInitializer;
       parser.parseGenericMethodComments = analysisOptions.strongMode;
       CompilationUnit unit = parser.parseCompilationUnit(token);
       unit.lineInfo = lineInfo;
+
+      // StringToken uses a static instance of StringCanonicalizer, so we need
+      // to clear it explicitly once we are done using it for this file.
+      StringToken.canonicalizer.clear();
+
       return unit;
     }
   }
 
   /**
    * Return `true` if the given byte lists are equal.
    */
   static bool _equalByteLists(List<int> a, List<int> b) {
     if (a == null) {
       return b == null;
@@ skipping 251 matching lines @@
         .where((f) => f._transitiveFiles == null)
         .toSet();
   }
 
   Set<FileState> get filesWithoutTransitiveSignature {
     return state._uriToFile.values
         .where((f) => f._transitiveSignature == null)
         .toSet();
   }
 }