Modified inaccurate comments for tryparse to be more precise.

Change-Id: Ib748d6fcaa3c1601d663ddf574a838dddf62a94b
Reviewed-on: https://dart-review.googlesource.com/c/88304
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
Commit-Queue: Zichang Guo <zichangguo@google.com>
diff --git a/sdk/lib/core/int.dart b/sdk/lib/core/int.dart
index 6964269..69b3eae 100644
--- a/sdk/lib/core/int.dart
+++ b/sdk/lib/core/int.dart
@@ -346,8 +346,8 @@
   /**
    * Parse [source] as a, possibly signed, integer literal and return its value.
    *
-   * Like [parse] except that this function returns `null` for invalid inputs
-   * instead of throwing.
+   * Like [parse] except that this function returns `null` where a
+   * similar call to [parse] would throw a [FormatException].
    */
   external static int tryParse(String source, {int radix});
 }