Don't cache result for homeDirPath. (flutter#27873)

Author: kangwang1988

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

@@ -7,16 +7,14 @@ import 'platform.dart';
 
 /// Return the absolute path of the user's home directory
 String get homeDirPath {
-  if (_homeDirPath == null) {
-    _homeDirPath = platform.isWindows
-        ? platform.environment['USERPROFILE']
-        : platform.environment['HOME'];
-    if (_homeDirPath != null)
-      _homeDirPath = fs.path.absolute(_homeDirPath);
+  String path = platform.isWindows
+      ? platform.environment['USERPROFILE']
+      : platform.environment['HOME'];
+  if (path != null) {
+    path = fs.path.absolute(path);
   }
-  return _homeDirPath;
+  return path;
 }
-String _homeDirPath;
 
 /// Throw a specialized exception for expected situations
 /// where the tool should exit with a clear message to the user