Fix Gradle lockfiles. (#137190)

dev/tools/bin/generate_gradle_lockfiles.dart

@@ -4,6 +4,7 @@
 
 // This script generates `android/build.gradle` for each directory specify in the stdin.
 // Then it generate the lockfiles for each Gradle project.
+// Prerequisite: make sure `flutter doctor -v` outputs the same version of java as `java --version`.
 // To regenerate these files, run `find . -type d -name 'android' | dart dev/tools/bin/generate_gradle_lockfiles.dart`
 
 import 'dart:io';
@@ -193,15 +194,24 @@ const String settingGradleFile = r'''
 // To update all the settings.gradle files in the Flutter repo,
 // See dev/tools/bin/generate_gradle_lockfiles.dart.
 
-include ':app'
+pluginManagement {
+    def flutterSdkPath = {
+        def properties = new Properties()
+        file("local.properties").withInputStream { properties.load(it) }
+        def flutterSdkPath = properties.getProperty("flutter.sdk")
+        assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
+        return flutterSdkPath
+    }
+    settings.ext.flutterSdkPath = flutterSdkPath()
 
-def localPropertiesFile = new File(rootProject.projectDir, "local.properties")
-def properties = new Properties()
+    includeBuild("${settings.ext.flutterSdkPath}/packages/flutter_tools/gradle")
 
-assert localPropertiesFile.exists()
-localPropertiesFile.withReader("UTF-8") { reader -> properties.load(reader) }
+    plugins {
+        id "dev.flutter.flutter-gradle-plugin" version "1.0.0" apply false
+    }
+}
 
-def flutterSdkPath = properties.getProperty("flutter.sdk")
-assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
-apply from: "$flutterSdkPath/packages/flutter_tools/gradle/app_plugin_loader.gradle"
+include ":app"
+
+apply from: "${settings.ext.flutterSdkPath}/packages/flutter_tools/gradle/app_plugin_loader.gradle"
 ''';