Fix control flow graph in the presence of aborting instructions in a try/catch/finally.

sdk/lib/_internal/compiler/implementation/ssa/tracer.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/tracer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/tracer.dart	(revision 14518)
+++ sdk/lib/_internal/compiler/implementation/ssa/tracer.dart	(working copy)
@@ -458,6 +458,10 @@
     return visitInvokeStatic(node);
   }
 
+  String visitExitTry(HExitTry node) {
+    return "Exit try";
+  }
+
   String visitTry(HTry node) {
     List<HBasicBlock> successors = currentBlock.successors;
     String tryBlock = 'B${successors[0].id}';