refactor to move an ios specific class out of globals.dart

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

diff --git a/packages/flutter_tools/lib/src/ios/mac.dart b/packages/flutter_tools/lib/src/ios/mac.dart
index 163f6f4..df2ef7d 100644
--- a/packages/flutter_tools/lib/src/ios/mac.dart
+++ b/packages/flutter_tools/lib/src/ios/mac.dart
@@ -18,15 +18,12 @@
 
 String get homeDirectory => path.absolute(Platform.environment['HOME']);
 
-// TODO(devoncarew): Refactor functionality into XCode.
-
 const int kXcodeRequiredVersionMajor = 7;
 const int kXcodeRequiredVersionMinor = 2;
 
 class XCode {
-  static void initGlobal() {
-    context[XCode] = new XCode();
-  }
+  /// Returns [XCode] active in the current app context.
+  static XCode get instance => context[XCode] ?? (context[XCode] = new XCode());
 
   bool get isInstalledAndMeetsVersionCheck => isInstalled && xcodeVersionSatisfactory;