Add file identifiers to summaries.

pkg/analyzer/test/src/summary/flat_buffers_test.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 test.src.summary.flat_buffers_test;
 
 import 'dart:typed_data';
 
 import 'package:analyzer/src/summary/flat_buffers.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 37 matching lines @@
   }
 
   void test_error_writeString_duringTable() {
     Builder builder = new Builder();
     builder.startTable();
     expect(() {
       builder.writeString('12345');
     }, throwsStateError);
   }
 
+  void test_file_identifier() {
+    Uint8List byteList;
+    {
+      Builder builder = new Builder(initialSize: 0);
+      builder.startTable();
+      Offset offset = builder.endTable();
+      byteList = builder.finish(offset, 'Az~ÿ');
+    }
+    // Convert byteList to a ByteData so that we can read data from it.
+    ByteData byteData = byteList.buffer.asByteData(byteList.offsetInBytes);
+    // First 4 bytes are an offset to the table data.
+    int tableDataLoc = byteData.getUint32(0, Endianness.LITTLE_ENDIAN);
+    // Next 4 bytes are the file identifier.
+    expect(byteData.getUint8(4), 65); // 'a'
+    expect(byteData.getUint8(5), 122); // 'z'
+    expect(byteData.getUint8(6), 126); // '~'
+    expect(byteData.getUint8(7), 255); // 'ÿ'
+    // First 4 bytes of the table data are a backwards offset to the vtable.
+    int vTableLoc = tableDataLoc -
+        byteData.getInt32(tableDataLoc, Endianness.LITTLE_ENDIAN);
+    // First 2 bytes of the vtable are the size of the vtable in bytes, which
+    // should be 4.
+    expect(byteData.getUint16(vTableLoc, Endianness.LITTLE_ENDIAN), 4);
+    // Next 2 bytes are the size of the object in bytes (including the vtable
+    // pointer), which should be 4.
+    expect(byteData.getUint16(vTableLoc + 2, Endianness.LITTLE_ENDIAN), 4);
+  }
+
   void test_low() {
     Builder builder = new Builder(initialSize: 0);
     builder.lowReset();
     expect((builder..lowWriteUint8(1)).lowFinish(), [1]);
     expect((builder..lowWriteUint32(2)).lowFinish(), [2, 0, 0, 0, 0, 0, 0, 1]);
     expect((builder..lowWriteUint8(3)).lowFinish(),
         [0, 0, 0, 3, 2, 0, 0, 0, 0, 0, 0, 1]);
     expect((builder..lowWriteUint8(4)).lowFinish(),
         [0, 0, 4, 3, 2, 0, 0, 0, 0, 0, 0, 1]);
     expect((builder..lowWriteUint8(5)).lowFinish(),
@@ skipping 257 matching lines @@
 }
 
 class TestPointReader extends TableReader<TestPointImpl> {
   const TestPointReader();
 
   @override
   TestPointImpl createObject(BufferPointer object) {
     return new TestPointImpl(object);
   }
 }