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

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
===================================================================
--- lib/compiler/implementation/ssa/codegen.dart	(revision 8084)
+++ lib/compiler/implementation/ssa/codegen.dart	(working copy)
@@ -726,7 +726,7 @@
       HParameterValue exception = info.catchVariable;
       String name = temporary(exception);
       parameterNames[exception.element] = name;
-      buffer.add('catch ($name) {\n');
+      buffer.add(' catch ($name) {\n');
       indent++;
       generateStatements(info.catchBlock);
       parameterNames.remove(exception.element);