[Gallery] Fix directory structure (#312)

gallery/lib/themes/material_demo_theme_data.dart

@@ -0,0 +1,57 @@
+// 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/foundation.dart';
+import 'package:flutter/material.dart';
+
+class MaterialDemoThemeData {
+  static final themeData = ThemeData(
+    colorScheme: _colorScheme,
+    appBarTheme: AppBarTheme(
+      color: _colorScheme.primary,
+      iconTheme: IconThemeData(color: _colorScheme.onPrimary),
+    ),
+    bottomAppBarTheme: BottomAppBarTheme(
+      color: _colorScheme.primary,
+    ),
+    buttonTheme: ButtonThemeData(
+      textTheme: ButtonTextTheme.primary,
+      colorScheme: _colorScheme,
+    ),
+    canvasColor: _colorScheme.background,
+    cursorColor: _colorScheme.primary,
+    toggleableActiveColor: _colorScheme.primary,
+    highlightColor: Colors.transparent,
+    indicatorColor: _colorScheme.onPrimary,
+    primaryColor: _colorScheme.primary,
+    accentColor: _colorScheme.primary,
+    backgroundColor: Colors.white,
+    scaffoldBackgroundColor: _colorScheme.background,
+    snackBarTheme: SnackBarThemeData(
+      behavior: SnackBarBehavior.floating,
+    ),
+    typography: Typography(
+      platform: defaultTargetPlatform,
+      englishLike: Typography.englishLike2018,
+      dense: Typography.dense2018,
+      tall: Typography.tall2018,
+    ),
+  );
+
+  static const _colorScheme = ColorScheme(
+    primary: Color(0xFF6200EE),
+    primaryVariant: Color(0xFF6200EE),
+    secondary: Color(0xFFFF5722),
+    secondaryVariant: Color(0xFFFF5722),
+    background: Colors.white,
+    surface: Color(0xFFF2F2F2),
+    onBackground: Colors.black,
+    onSurface: Colors.black,
+    error: Colors.red,
+    onError: Colors.white,
+    onPrimary: Colors.white,
+    onSecondary: Colors.white,
+    brightness: Brightness.light,
+  );
+}