[Gallery] Fix directory structure (#312)

gallery/lib/layout/adaptive.dart

@@ -0,0 +1,36 @@
+// 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 'package:flutter/material.dart';
+
+enum DisplayType {
+  desktop,
+  mobile,
+}
+
+const _desktopBreakpoint = 700.0;
+const _smallDesktopMaxWidth = 1000.0;
+
+/// Returns the [DisplayType] for the current screen. This app only supports
+/// mobile and desktop layouts, and as such we only have one breakpoint.
+DisplayType displayTypeOf(BuildContext context) {
+  if (MediaQuery.of(context).size.shortestSide > _desktopBreakpoint) {
+    return DisplayType.desktop;
+  } else {
+    return DisplayType.mobile;
+  }
+}
+
+/// Returns a boolean if we are in a display of [DisplayType.desktop]. Used to
+/// build adaptive and responsive layouts.
+bool isDisplayDesktop(BuildContext context) {
+  return displayTypeOf(context) == DisplayType.desktop;
+}
+
+/// Returns a boolean if we are in a display of [DisplayType.desktop] but less
+/// than 1000 width. Used to build adaptive and responsive layouts.
+bool isDisplaySmallDesktop(BuildContext context) {
+  return isDisplayDesktop(context) &&
+      MediaQuery.of(context).size.width < _smallDesktopMaxWidth;
+}