add tool to get breakdown of deferred libraries by size

bin/deferred_library_size.dart

Index: bin/deferred_library_size.dart
diff --git a/bin/deferred_library_size.dart b/bin/deferred_library_size.dart
new file mode 100644
index 0000000000000000000000000000000000000000..349459ce6141e01724e22bc72508cd75a99f2bb8
--- /dev/null
+++ b/bin/deferred_library_size.dart
@@ -0,0 +1,76 @@
+// 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.
+
+/// This tool gives a breakdown of code size by deferred part in the program.
+library dart2js_info.bin.deferred_library_size;
+
+import 'dart:math';
+
+import 'package:dart2js_info/info.dart';
+import 'package:dart2js_info/src/util.dart';
+
+main(args) async {
+  // TODO(het): Would be faster to only parse the 'outputUnits' part
+  var info = await infoFromFile(args.first);
+  var sizeByImport = getSizeByImport(info);
+  printSizes(sizeByImport, info.program.size);
+}
+
+class ImportSize {
+  final String import;
+  final int size;
+
+  const ImportSize(this.import, this.size);
+
+  String toString() {
+    return '$import: $size';
+  }
+}
+
+void printSizes(Map<String, int> sizeByImport, int programSize) {
+  var importSizes = <ImportSize>[];
+  sizeByImport.forEach((import, size) {
+    importSizes.add(new ImportSize(import, size));
+  });
+  // Sort by size, largest first.
+  importSizes.sort((a, b) => b.size - a.size);
+  var longest = importSizes.fold('Percent of code deferred'.length,
+      (longest, importSize) => max(longest, importSize.import.length));
+
+  _printRow(label, data, {int width: 15}) {
+    print('${label.toString().padRight(longest + 1)}'
+        '${data.toString().padLeft(width)}');
+  }
+
+  print('');
+  print('Size by library');
+  print('-' * (longest + 16));
+  for (var importSize in importSizes) {
+    // TODO(het): split into specific and shared size
+    _printRow(importSize.import, importSize.size);
+  }
+  print('-' * (longest + 16));
+
+  var mainChunkSize = sizeByImport['main'];
+  var deferredSize = programSize - mainChunkSize;
+  var percentDeferred = (deferredSize * 100 / programSize).toStringAsFixed(2);
+  _printRow('Main chunk size', mainChunkSize);
+  _printRow('Deferred code size', deferredSize);
+  _printRow('Percent of code deferred', '$percentDeferred%');
+}
+
+Map<String, int> getSizeByImport(AllInfo info) {
+  var sizeByImport = <String, int>{};
+  for (var outputUnit in info.outputUnits) {
+    if (outputUnit.name == 'main' || outputUnit.name == null) {
+      sizeByImport['main'] = outputUnit.size;
+    } else {
+      for (var import in outputUnit.imports) {
+        sizeByImport.putIfAbsent(import, () => 0);
+        sizeByImport[import] += outputUnit.size;
+      }
+    }
+  }
+  return sizeByImport;
+}