Repository: flutter
Issue: Text does not conform to DefaultTextStyle which is beyond Scaffold
Labels: framework,a: internationalization,a: typography,has reproducible steps,P2,found in release: 2.5,found in release: 2.6,team-framework,triaged-framework

## Steps to Reproduce

`Text` does not conform to `DefaultTextStyle` which is beyond `Scaffold`.

I am using `DefaultTextStyle` to set default `Locale` to all text. I would like to set `DefaultTextStyle` at the root of the application instead of setting each `Text`.

In the following example, `Text` does not conform to locale. Also, it does not conform color too. Because `Scaffold` uses `DefaultTextStyle` internally and the style is not inherited.

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    home: new FooPage(),
  ));
}

class FooPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return new FooPageState();
  }
}

class FooPageState extends State<FooPage> {
  String _language = "ja";
  String _country = "JP";
  
  @override
  Widget build(BuildContext context) {
    return new DefaultTextStyle(
      style: new TextStyle(
        color: Colors.blue,
        locale: new Locale(_language, _country),
      ),
      child: new Scaffold(
        appBar: new AppBar(title: new Text("CJK Fonts")),
        body: new Center(
          child: new Column(
            children: <Widget>[
              new Text("累令直刃漢"),
              new RaisedButton(
                onPressed: () {
                  setLocale("ja", "JP");
                },
                child: new Text("ja-JP"),
              ),
              new RaisedButton(
                onPressed: () {
                  setLocale("zh", "CN");
                },
                child: new Text("zh-CN"),
              ),
              new RaisedButton(
                onPressed: () {
                  setLocale("zh", "TW");
                },
                child: new Text("zh-TW"),
              ),
              new RaisedButton(
                onPressed: () {
                  setLocale("ko", "KR");
                },
                child: new Text("ko-KR"),
              ),
              new RaisedButton(
                onPressed: () {
                  setLocale("vi", "VN");
                },
                child: new Text("vi-VN"),
              ),
            ],
          ),
        ),
      ),
    );
  }
  
  void setLocale(String la, String co) {
    setState(() {
      _language = la;
      _country = co;
    });
  }
}
```

If you set the TextStyle with locale directly to Text, it works.

## Logs

No errors.

```
[✓] Flutter (Channel dev, v0.4.2, on Mac OS X 10.12.6 16G1314, locale ja-JP)
    • Flutter version 0.4.2 at /Applications/flutter
    • Framework revision de332ec782 (3 days ago), 2018-05-07 14:13:53 -0700
    • Engine revision e976be13c5
    • Dart version 2.0.0-dev.53.0.flutter-e6d7d67f4b

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
    • Android SDK at /Users/najeira/Library/Android/sdk
    • Android NDK at /Users/najeira/Library/Android/sdk/ndk-bundle
    • Platform android-27, build-tools 27.0.3
    • ANDROID_HOME = /Users/najeira/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-915-b08)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.2)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 9.2, Build version 9C40b
    • ios-deploy 1.9.2
    • CocoaPods version 1.4.0

[✓] Android Studio (version 3.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    • Dart plugin version 171.4424
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-915-b08)

[✓] IntelliJ IDEA Ultimate Edition (version 2018.1)
    • IntelliJ at /Applications/IntelliJ IDEA.app
    • Flutter plugin version 23.1.3
    • Dart plugin version 181.4203.498

[✓] VS Code (version 1.23.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Dart Code extension version 2.12.1
```