*FlutterFireを初期化するには、FirebaseクラスのinitializeAppメソッドを呼び出します
==[https://firebase.flutter.dev/docs/auth/overview/ Authentication]==
===Stableチャネルに切り替え===
<pre>
$ flutter channel stable
Switching to flutter channel 'stable'...
git: From https://github.com/flutter/flutter
git: + 2b9537c783...cc00e7e6bc dev -> origin/dev (forced update)
git: * [new branch] dnfield-patch-1 -> origin/dnfield-patch-1
git: * [new branch] flutter-2.4-candidate.1 -> origin/flutter-2.4-candidate.1
git: * [new branch] flutter-2.4-candidate.2 -> origin/flutter-2.4-candidate.2
git: * [new branch] flutter-2.4-candidate.3 -> origin/flutter-2.4-candidate.3
git: * [new branch] flutter-2.4-candidate.4 -> origin/flutter-2.4-candidate.4
git: * [new branch] flutter-2.4-candidate.5 -> origin/flutter-2.4-candidate.5
git: 52e2ca38fc..2108fbd78d master -> origin/master
git: + c8311f68be...f4d2c79a6a revert-85466-revert-85221-0624new -> origin/revert-85466-revert-85221-0624new (forced update)
git: * [new branch] revert-86171-revert-83924-textTheme -> origin/revert-86171-revert-83924-textTheme
git: * [new branch] revert-86198-deprecate_appbar_backwards_compatibility_flag -> origin/revert-86198-deprecate_appbar_backwards_compatibility_flag
git: * [new branch] test -> origin/test
git: * [new branch] test2 -> origin/test2
git: * [new tag] 2.4.0-0.0.pre -> 2.4.0-0.0.pre
git: * [new tag] 2.4.0-4.0.pre -> 2.4.0-4.0.pre
git: Already on 'stable'
git: Your branch is up to date with 'origin/stable'.
Successfully switched to flutter channel 'stable'.
To ensure that you're on the latest build from this channel, run 'flutter upgrade'
</pre>