Don't check in benchmark sources.

.gitignore

@@ -7,3 +7,4 @@ build/
 packages
 .packages
 pubspec.lock
+/benchmark/source

benchmark/generate.dart

@@ -0,0 +1,31 @@
+#!/usr/bin/env dart
+// Copyright 2016 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:async';
+import 'dart:io';
+import 'dart:math' as math;
+
+main() async {
+  var sources = new Directory("benchmark/source");
+  if (!await sources.exists()) await sources.create();
+
+  await writeNTimes("${sources.path}/small_plain.scss", ".foo {a: b}", 4);
+  await writeNTimes("${sources.path}/large_plain.scss", ".foo {a: b}", math.pow(2, 17));
+  await writeNTimes("${sources.path}/preceding_sparse_extend.scss", ".foo {a: b}", math.pow(2, 17), header: '.x {@extend .y}', footer: '.y {a: b}');
+  await writeNTimes("${sources.path}/following_sparse_extend.scss", ".foo {a: b}", math.pow(2, 17), header: '.y {a: b}', footer: '.x {@extend .y}');
+  await writeNTimes("${sources.path}/preceding_dense_extend.scss", ".foo {a: b}", math.pow(2, 17), header: '.bar {@extend .foo}');
+  await writeNTimes("${sources.path}/following_dense_extend.scss", ".foo {a: b}", math.pow(2, 17), footer: '.bar {@extend .foo}');
+}
+
+Future writeNTimes(String path, String text, int times, {String header, String footer}) async {
+  print("Generating $path...");
+  var file = new File(path).openWrite();
+  if (header != null) file.writeln(header);
+  for (var i = 0; i < times; i++) {
+    file.writeln(text);
+  }
+  if (footer != null) file.writeln(footer);
+  await file.close();
+}

benchmark/source/small_plain.scss

@@ -1,4 +0,0 @@
-.foo {a: b}
-.foo {a: b}
-.foo {a: b}
-.foo {a: b}