[Gallery] Fix directory structure (#312)

gallery/lib/layout/text_scale.dart

@@ -0,0 +1,42 @@
+// Copyright 2019 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+
+import 'package:gallery/data/gallery_options.dart';
+
+double _textScaleFactor(BuildContext context) {
+  return GalleryOptions.of(context).textScaleFactor(context);
+}
+
+// When text is larger, this factor becomes larger, but at half the rate.
+//
+// | Text scaling | Text scale factor | reducedTextScale(context) |
+// |--------------|-------------------|---------------------------|
+// | Small        |               0.8 |                       1.0 |
+// | Normal       |               1.0 |                       1.0 |
+// | Large        |               2.0 |                       1.5 |
+// | Huge         |               3.0 |                       2.0 |
+
+double reducedTextScale(BuildContext context) {
+  double textScaleFactor = _textScaleFactor(context);
+  return textScaleFactor >= 1 ? (1 + textScaleFactor) / 2 : 1;
+}
+
+// When text is larger, this factor becomes larger at the same rate.
+// But when text is smaller, this factor stays at 1.
+//
+// | Text scaling | Text scale factor |  cappedTextScale(context) |
+// |--------------|-------------------|---------------------------|
+// | Small        |               0.8 |                       1.0 |
+// | Normal       |               1.0 |                       1.0 |
+// | Large        |               2.0 |                       2.0 |
+// | Huge         |               3.0 |                       3.0 |
+
+double cappedTextScale(BuildContext context) {
+  double textScaleFactor = _textScaleFactor(context);
+  return max(textScaleFactor, 1);
+}