Support parsing empty stack chains.

lib/src/chain.dart

Index: lib/src/chain.dart
diff --git a/lib/src/chain.dart b/lib/src/chain.dart
index 87cc6be99336c8a6535d575074e63a3dc5c8c1c0..3e2100e46340544d87c1e1c1753f892cdda50596 100644
--- a/lib/src/chain.dart
+++ b/lib/src/chain.dart
@@ -127,8 +127,11 @@ class Chain implements StackTrace {
   /// Parses a string representation of a stack chain.
   ///
   /// Specifically, this parses the output of [Chain.toString].
-  factory Chain.parse(String chain) =>
-    new Chain(chain.split(_gap).map((trace) => new Trace.parseFriendly(trace)));
+  factory Chain.parse(String chain) {
+    if (chain.isEmpty) return new Chain([]);
+    return new Chain(
+        chain.split(_gap).map((trace) => new Trace.parseFriendly(trace)));
+  }
 
   /// Returns a new [Chain] comprised of [traces].
   Chain(Iterable<Trace> traces)