Make Flutter tooling work on Android without Xcode being installed (#15161)

packages/flutter_tools/lib/src/ios/xcodeproj.dart

diff --git a/packages/flutter_tools/lib/src/ios/xcodeproj.dart b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
index 9a50d30..e35d6aa 100644
--- a/packages/flutter_tools/lib/src/ios/xcodeproj.dart
+++ b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
@@ -7,7 +7,10 @@
 import '../artifacts.dart';
 import '../base/context.dart';
 import '../base/file_system.dart';
+import '../base/io.dart';
+import '../base/platform.dart';
 import '../base/process.dart';
+import '../base/process_manager.dart';
 import '../base/utils.dart';
 import '../build_info.dart';
 import '../cache.dart';
@@ -84,16 +87,58 @@
 
 XcodeProjectInterpreter get xcodeProjectInterpreter => context.putIfAbsent(
   XcodeProjectInterpreter,
-  () => const XcodeProjectInterpreter(),
+  () => new XcodeProjectInterpreter(),
 );
 
-/// Interpreter of Xcode projects settings.
+/// Interpreter of Xcode projects.
 class XcodeProjectInterpreter {
   static const String _executable = '/usr/bin/xcodebuild';
+  static final RegExp _versionRegex = new RegExp(r'Xcode ([0-9.]+)');
 
-  const XcodeProjectInterpreter();
+  void _updateVersion() {
+    if (!platform.isMacOS || !fs.file(_executable).existsSync()) {
+      return;
+    }
+    try {
+      final ProcessResult result = processManager.runSync(<String>[_executable, '-version']);
+      if (result.exitCode != 0) {
+        return;
+      }
+      _versionText = result.stdout.trim().replaceAll('\n', ', ');
+      final Match match = _versionRegex.firstMatch(versionText);
+      if (match == null)
+        return;
+      final String version = match.group(1);
+      final List<String> components = version.split('.');
+      _majorVersion = int.parse(components[0]);
+      _minorVersion = components.length == 1 ? 0 : int.parse(components[1]);
+    } on ProcessException {
+      // Ignore: leave values null.
+    }
+  }
 
-  bool get canInterpretXcodeProjects => fs.isFileSync(_executable);
+  bool get isInstalled => majorVersion != null;
+
+  String _versionText;
+  String get versionText {
+    if (_versionText == null)
+      _updateVersion();
+    return _versionText;
+  }
+
+  int _majorVersion;
+  int get majorVersion {
+    if (_majorVersion == null)
+      _updateVersion();
+    return _majorVersion;
+  }
+
+  int _minorVersion;
+  int get minorVersion {
+    if (_minorVersion == null)
+      _updateVersion();
+    return _minorVersion;
+  }
 
   Map<String, String> getBuildSettings(String projectPath, String target) {
     final String out = runCheckedSync(<String>[