Avoid overwriting chain for trace if one exists (dart-lang/stack_trace#37)

pkgs/stack_trace/CHANGELOG.md

diff --git a/pkgs/stack_trace/CHANGELOG.md b/pkgs/stack_trace/CHANGELOG.md
index 18ffda8..2627e71 100644
--- a/pkgs/stack_trace/CHANGELOG.md
+++ b/pkgs/stack_trace/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.9.1
+* Preserve the original chain for a trace to handle cases where an
+  error is rethrown.
+
 ## 1.9.0
 
 * Add an `errorZone` parameter to `Chain.capture()` that makes it avoid creating

pkgs/stack_trace/lib/src/stack_zone_specification.dart

diff --git a/pkgs/stack_trace/lib/src/stack_zone_specification.dart b/pkgs/stack_trace/lib/src/stack_zone_specification.dart
index 5be8dd3..6c31d12 100644
--- a/pkgs/stack_trace/lib/src/stack_zone_specification.dart
+++ b/pkgs/stack_trace/lib/src/stack_zone_specification.dart
@@ -208,7 +208,10 @@
     try {
       return f();
     } catch (e, stackTrace) {
-      _chains[stackTrace] = node;
+      // We can see the same stack trace multiple times if it's rethrown through
+      // guarded callbacks.  The innermost chain will have the most
+      // information so it should take precedence.
+      _chains[stackTrace] ??= node;
       rethrow;
     } finally {
       _currentNode = previousNode;

pkgs/stack_trace/pubspec.yaml

diff --git a/pkgs/stack_trace/pubspec.yaml b/pkgs/stack_trace/pubspec.yaml
index 3218be1..f7c562d 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: 1.9.0
+version: 1.9.1
 author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/stack_trace
 description: A package for manipulating stack traces and printing them readably.