コンパイル時にエラーが発生します。 flutter、firebaseアプリ（Android Studioで開発）

アプリをRunで起動すると、下記のようなエラーが出ます。

●エラー内容

Launching lib\main.dart on Android SDK built for x86 in debug mode...
Initializing gradle...
Resolving dependencies...
Finished with error: Please review your Gradle project setup in the android/ folder.

Error running Gradle:
ProcessException: Process "C:\Users\\AndroidStudioProjects\flutter_app2\android\gradlew.bat" exited abnormally:
FAILURE: Build failed with an exception.

• Where:
  Build file 'C:\Users\\AndroidStudioProjects\flutter_app2\android\build.gradle' > line: 24

• What went wrong:
  A problem occurred evaluating root project 'android'.
  A problem occurred configuring project ':app'.
  Could not resolve all artifacts for configuration ':app:classpath'.
  Cannot resolve external dependency com.google.gms:google-services:4.0.1 because no repositories are defined.
  Required by:
  project :app

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https://help.gradle.org

BUILD FAILED in 1s
Command: C:\Users\\AndroidStudioProjects\flutter_app2\android\gradlew.bat app:properties

build.gradleファイル内に、下記の内容を記載しない場合はエラーは発生しないので、この部分がエラーの原因と思われますが、対応方法などご教授いただけると大変助かります。

buildscript {
dependencies {
    // Add this line
    classpath 'com.google.gms:google-services:4.0.1'
    }
}
allprojects {
    // ...
    repositories {
        google() // Google's Maven repository
        // ...
    }
}

apply plugin: 'com.android.application'

android {
    // ...
}

dependencies {
    // ...
    implementation 'com.google.firebase:firebase-core:16.0.1'
    // Getting a "Could not find" error? Make sure you have
    // added the Google maven respository to your root build.gradle
}

// ADD THIS AT THE BOTTOM
apply plugin: 'com.google.gms.google-services'

●build.gradleファイル内容

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

def flutterRoot = localProperties.getProperty('flutter.sdk')
if (flutterRoot == null) {
    throw new GradleException("Flutter SDK not found. Define location with flutt    er.sdk in the local.properties file.")
}

def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
if (flutterVersionCode == null) {
    flutterVersionCode = '1'
}

def flutterVersionName = localProperties.getProperty('flutter.versionName')
if (flutterVersionName == null) {
    flutterVersionName = '1.0'
}

apply plugin: 'com.android.application'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"

android {
    compileSdkVersion 28

    lintOptions {
        disable 'InvalidPackage'
    }

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.andro    id.com/studio/build/application-id.html).
        applicationId "com.example.androidstudio.flutter_app2"
        minSdkVersion 16
        targetSdkVersion 28
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunne    r"
    }

    buildTypes {
        release {
            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` w    orks.
            signingConfig signingConfigs.debug
        }
    }
}

flutter {
    source '../..'
}

dependencies {
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3    .0.2'
}


buildscript {
    dependencies {
        // Add this line
        classpath 'com.google.gms:google-services:4.0.1'
    }
}
allprojects {
    // ...
    repositories {
        google() // Google's Maven repository
        // ...
    }
}

apply plugin: 'com.android.application'

android {
    // ...
}

dependencies {
    // ...
    implementation 'com.google.firebase:firebase-core:16.0.1'
    // Getting a "Could not find" error? Make sure you have
    // added the Google maven respository to your root build.gradle
}

// ADD THIS AT THE BOTTOM
apply plugin: 'com.google.gms.google-services'