Add file identifiers to summaries.

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 228 matching lines @@
     // Set the VTable offset.
     _setInt32AtTail(_buf, tableTail, vTableTail - tableTail);
     // Done with this table.
     _currentVTable = null;
     return new Offset(tableTail);
   }
 
   /**
    * Finish off the creation of the buffer.  The given [offset] is used as the
    * root object offset, and usually references directly or indirectly every
-   * written object.
+   * written object.  If [fileIdentifier] is specified (and not `null`), it is
+   * interpreted as a 4-byte Latin-1 encoded string that should be placed at
+   * bytes 4-7 of the file.
    */
-  Uint8List finish(Offset offset) {
-    _prepare(max(4, _maxAlign), 1);
+  Uint8List finish(Offset offset, [String fileIdentifier]) {
+    _prepare(max(4, _maxAlign), fileIdentifier == null ? 1 : 2);
     int alignedTail = _tail + ((-_tail) % _maxAlign);
     _setUint32AtTail(_buf, alignedTail, alignedTail - offset._tail);
+    if (fileIdentifier != null) {
+      for (int i = 0; i < 4; i++) {
+        _setUint8AtTail(
+            _buf, alignedTail - 4 - i, fileIdentifier.codeUnitAt(i));
+      }
+    }
     return _buf.buffer.asUint8List(_buf.lengthInBytes - alignedTail);
   }
 
   /**
    * This is a low-level method, it should not be invoked by clients.
    */
   Uint8List lowFinish() {
     int alignedTail = _tail + ((-_tail) % _maxAlign);
     return _buf.buffer.asUint8List(_buf.lengthInBytes - alignedTail);
   }
@@ skipping 567 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;
     }
   }
 }