Fix a syntax error.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1834263004 .

pkgs/stack_trace/CHANGELOG.md

diff --git a/pkgs/stack_trace/CHANGELOG.md b/pkgs/stack_trace/CHANGELOG.md
index a23eebd..75a311f 100644
--- a/pkgs/stack_trace/CHANGELOG.md
+++ b/pkgs/stack_trace/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.6.4
+
+* Fix a syntax error introduced in 1.6.3.
+
 ## 1.6.3
 
 * Make `Chain.capture()` generic. Its signature is now `T Chain.capture<T>(T

pkgs/stack_trace/lib/src/chain.dart

diff --git a/pkgs/stack_trace/lib/src/chain.dart b/pkgs/stack_trace/lib/src/chain.dart
index b436651..6de670f 100644
--- a/pkgs/stack_trace/lib/src/chain.dart
+++ b/pkgs/stack_trace/lib/src/chain.dart
@@ -68,7 +68,7 @@
   /// considered unhandled.
   ///
   /// If [callback] returns a value, it will be returned by [capture] as well.
-  static /*=T*? capture/*<T>*/(/*=T*/ callback(),
+  static /*=T*/ capture/*<T>*/(/*=T*/ callback(),
       {void onError(error, Chain chain), bool when: true}) {
     if (!when) {
       var newOnError;

pkgs/stack_trace/pubspec.yaml

diff --git a/pkgs/stack_trace/pubspec.yaml b/pkgs/stack_trace/pubspec.yaml
index ce1d39d..654d13d 100644
--- a/pkgs/stack_trace/pubspec.yaml
+++ b/pkgs/stack_trace/pubspec.yaml
@@ -7,7 +7,7 @@
 #
 # When the major version is upgraded, you *must* update that version constraint
 # in pub to stay in sync with this.
-version: 1.6.3
+version: 1.6.4
 author: "Dart Team <misc@dartlang.org>"
 homepage: http://github.com/dart-lang/stack_trace
 description: >