Japanese default font family is incorrect on iOS 12

[mono0926]

Steps to Reproduce

1. Run the Flutter application which contains Japanese(such as Text('追加')) on iOS 12(simulator or physical device).
2. Font family is weird(not Japanese system font).
   • See Image A
3. If specified to TextStyle(fontFamily: 'Hiragino Kaku Gothic ProN')), it looks well.
   • See Image B

Image A(Incorrect)	Image B(Correct)

You can check by this: https://github.com/mono0926/wdb106-flutter

If run on under iOS 11, there are no problems even though fontFamily is omitted.

Doctor

➜  flutter doctor -v
[✓] Flutter (Channel master, v0.8.2-pre.23, on Mac OS X 10.14 18A384a, locale en-JP)
    • Flutter version 0.8.2-pre.23 at /Users/mono/Git/Lib/flutter
    • Framework revision bb7735e8f9 (3 days ago), 2018-09-08 22:04:32 -0400
    • Engine revision 5c1a826eec
    • Dart version 2.1.0-dev.4.0.flutter-cd9a42239f

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
    • Android SDK at /Users/mono/Library/Android/sdk
    • Android NDK at /Users/mono/Library/Android/sdk/ndk-bundle
    • Platform android-27, build-tools 27.0.3
    • 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-1024-b01)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 10.0)
    • Xcode at /Applications/Xcode-beta.app/Contents/Developer
    • Xcode 10.0, Build version 10L232m
    • ios-deploy 1.9.2
    • CocoaPods version 1.5.3

[✓] Android Studio (version 3.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 27.1.1
    • Dart plugin version 173.4700
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[✓] VS Code (version 1.27.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 2.18.0

[✓] Connected devices (4 available)
    • monoyagon      • 74df57781baa272bb902fde8a1227cf3ee117a6f • ios • iOS 12.0
    • monoPhone7Plus • 617c4722cbfd94e1da694914683b5f43399e018d • ios • iOS 11.4.1
    • monoPhone      • 44f39637ca012b78a08b4e48d0959239dd8cb2b0 • ios • iOS 12.0
    • iPhone X       • 26F093E2-FC4E-4F05-8EB0-D1229CD11B3E     • ios • iOS 12.0 (simulator)

• No issues found!

[cbracken]

/cc @xster @GaryQian @jason-simmons

[mono0926]

Fixed now 👍
I want to know the cause and a fix commit if possible.

✗ flutter doctor -v
[✓] Flutter (Channel master, v0.9.7-pre.62, on Mac OS X 10.14 18A389, locale en-JP)
    • Flutter version 0.9.7-pre.62 at /Users/mono/Git/Lib/flutter
    • Framework revision 2c063b7ca5 (51 minutes ago), 2018-10-08 08:45:24 +0200
    • Engine revision 572fa5646a
    • Dart version 2.1.0-dev.6.0.flutter-c6254163dc

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
    • Android SDK at /Users/mono/Library/Android/sdk
    • Android NDK at /Users/mono/Library/Android/sdk/ndk-bundle
    • Platform android-27, build-tools 27.0.3
    • 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-1136-b06)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 10.0)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 10.0, Build version 10A255
    • ios-deploy 2.0.0
    • CocoaPods version 1.5.3

[✓] Android Studio (version 3.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 28.0.2
    • Dart plugin version 181.5616
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1136-b06)

[✓] VS Code (version 1.27.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 2.19.0

[✓] Connected device (2 available)
    • monoPhone7Plus • 617c4722cbfd94e1da694914683b5f43399e018d • ios • iOS 11.4.1
    • iPhone XS Max  • 81228107-2CC9-4A54-B158-AB8947930F6B     • ios • iOS 12.0 (simulator)

[github-actions]

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