Doc - Fix OSError.message and errorCode doc

Bug: https://github.com/dart-lang/sdk/issues/30698
Change-Id: Iae4ed07171862b44d1303fe1ba33a587b04e5aa5
Reviewed-on: https://dart-review.googlesource.com/61981
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
diff --git a/sdk/lib/io/common.dart b/sdk/lib/io/common.dart
index 852a267..10f3c39 100644
--- a/sdk/lib/io/common.dart
+++ b/sdk/lib/io/common.dart
@@ -53,16 +53,14 @@
   /** Constant used to indicate that no OS error code is available. */
   static const int noErrorCode = -1;
 
-  /**
-    * Error message supplied by the operating system. null if no message is
-    * associated with the error.
-    */
+  /// Error message supplied by the operating system. This may be `null` or
+  /// empty if no message is associated with the error.
   final String message;
 
-  /**
-    * Error code supplied by the operating system. Will have the value
-    * [noErrorCode] if there is no error code associated with the error.
-    */
+  /// Error code supplied by the operating system.
+  ///
+  /// Will have the value [OSError.noErrorCode] if there is no error code
+  /// associated with the error.
   final int errorCode;
 
   /** Creates an OSError object from a message and an errorCode. */