Validate that all instructions dominate their inputs. And fix a bug where that did not happen.

lib/compiler/implementation/ssa/closure.dart

Index: lib/compiler/implementation/ssa/closure.dart
===================================================================
--- lib/compiler/implementation/ssa/closure.dart	(revision 8031)
+++ lib/compiler/implementation/ssa/closure.dart	(working copy)
@@ -436,8 +436,9 @@
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
+    bool oldInTryCatchOrFinally = inTryCatchOrFinally;
     inTryCatchOrFinally = true;
     node.visitChildren(this);
-    inTryCatchOrFinally = false;
+    inTryCatchOrFinally = oldInTryCatchOrFinally;
   }
 }