Detect Android SDK 28/28.0.3 (#26942)

* Detect Android SDK 28/28.0.3

* revert minimumAndroidSdkVersion const change

packages/flutter_tools/lib/src/android/android_workflow.dart

diff --git a/packages/flutter_tools/lib/src/android/android_workflow.dart b/packages/flutter_tools/lib/src/android/android_workflow.dart
index d1978a2..dfbc083 100644
--- a/packages/flutter_tools/lib/src/android/android_workflow.dart
+++ b/packages/flutter_tools/lib/src/android/android_workflow.dart
@@ -18,6 +18,9 @@
 import '../globals.dart';
 import 'android_sdk.dart';
 
+const int kAndroidSdkMinVersion = 28;
+final Version kAndroidSdkBuildToolsMinVersion = Version(28, 0, 3);
+
 AndroidWorkflow get androidWorkflow => context[AndroidWorkflow];
 AndroidValidator get androidValidator => context[AndroidValidator];
 AndroidLicenseValidator get androidLicenseValidator => context[AndroidLicenseValidator];
@@ -110,11 +113,19 @@
 
     String sdkVersionText;
     if (androidSdk.latestVersion != null) {
+      if (androidSdk.latestVersion.sdkLevel < 28 || androidSdk.latestVersion.buildToolsVersion < kAndroidSdkBuildToolsMinVersion) {
+        messages.add(ValidationMessage.error(
+          userMessages.androidSdkBuildToolsOutdated(androidSdk.sdkManagerPath, kAndroidSdkMinVersion, kAndroidSdkBuildToolsMinVersion.toString())),
+        );
+        return ValidationResult(ValidationType.missing, messages);
+      }
       sdkVersionText = userMessages.androidStatusInfo(androidSdk.latestVersion.buildToolsVersionName);
 
       messages.add(ValidationMessage(userMessages.androidSdkPlatformToolsVersion(
         androidSdk.latestVersion.platformName,
         androidSdk.latestVersion.buildToolsVersionName)));
+    } else {
+      messages.add(ValidationMessage.error(userMessages.androidMissingSdkInstructions(kAndroidHome)));
     }
 
     if (platform.environment.containsKey(kAndroidHome)) {
@@ -271,7 +282,7 @@
     final Version sdkManagerVersion = Version.parse(androidSdk.sdkManagerVersion);
     if (sdkManagerVersion == null || sdkManagerVersion.major < 26) {
       // SDK manager is found, but needs to be updated.
-      throwToolExit(userMessages.androidSdkOutdated(androidSdk.sdkManagerPath));
+      throwToolExit(userMessages.androidSdkManagerOutdated(androidSdk.sdkManagerPath));
     }
 
     final Process process = await runCommand(

packages/flutter_tools/lib/src/base/user_messages.dart

diff --git a/packages/flutter_tools/lib/src/base/user_messages.dart b/packages/flutter_tools/lib/src/base/user_messages.dart
index 2248d11..813247c 100644
--- a/packages/flutter_tools/lib/src/base/user_messages.dart
+++ b/packages/flutter_tools/lib/src/base/user_messages.dart
@@ -76,7 +76,7 @@
   String get androidLicensesSome => 'Some Android licenses not accepted.  To resolve this, run: flutter doctor --android-licenses';
   String get androidLicensesNone => 'Android licenses not accepted.  To resolve this, run: flutter doctor --android-licenses';
   String get androidLicensesUnknown => 'Android license status unknown.';
-  String androidSdkOutdated(String managerPath) =>
+  String androidSdkManagerOutdated(String managerPath) =>
       'A newer version of the Android SDK is required. To update, run:\n'
       '$managerPath --update\n';
   String androidLicensesTimeout(String managerPath) => 'Intentionally killing $managerPath';
@@ -85,6 +85,11 @@
       'Android sdkmanager tool not found ($sdkManagerPath).\n'
       'Try re-installing or updating your Android SDK,\n'
       'visit https://flutter.io/setup/#android-setup for detailed instructions.';
+  String androidSdkBuildToolsOutdated(String managerPath, int sdkMinVersion, String buildToolsMinVersion) =>
+      'Flutter requires Android SDK $sdkMinVersion and the Android BuildTools $buildToolsMinVersion\n'
+      'To update using sdkmanager, run:\n'
+      '  $managerPath "platforms;android-$sdkMinVersion" "build-tools;$buildToolsMinVersion"\n'
+      'or visit https://flutter.io/setup/#android-setup for detailed instructions.';
 
   // Messages used in AndroidStudioValidator
   String androidStudioVersion(String version) => 'version $version';