Use String.fromCharCodes() instead of UTF8.decode() for Latin strings.

pkg/analyzer/lib/src/summary/flat_buffers.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 analyzer.src.summary.flat_buffers;
 
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:math';
 import 'dart:typed_data';
@@ skipping 649 matching lines @@
 class StringReader extends Reader<String> {
   const StringReader() : super();
 
   @override
   int get size => 4;
 
   @override
   String read(BufferPointer ref) {
     BufferPointer object = ref.derefObject();
     int length = object._getUint32();
-    return UTF8
-        .decode(ref._buffer.buffer.asUint8List(object._offset + 4, length));
+    Uint8List bytes = ref._buffer.buffer.asUint8List(object._offset + 4, length);
+    if (_isLatin(bytes)) {
+      return new String.fromCharCodes(bytes);
+    }
+    return UTF8.decode(bytes);
+  }
+
+  static bool _isLatin(Uint8List bytes) {
+    int length = bytes.length;
+    for (int i = 0; i < length; i++) {
+      if (bytes[i] > 127) {
+        return false;
+      }
+    }
+    return true;
   }
 }
 
 /**
  * An abstract reader for tables.
  */
 abstract class TableReader<T> extends Reader<T> {
   const TableReader();
 
   @override
@@ skipping 253 matching lines @@
     // Table size.
     buf.setUint16(bufOffset, tableSize, Endianness.LITTLE_ENDIAN);
     bufOffset += 2;
     // Field offsets.
     for (int fieldOffset in fieldOffsets) {
       buf.setUint16(bufOffset, fieldOffset, Endianness.LITTLE_ENDIAN);
       bufOffset += 2;
     }
   }
 }