Add --verify-ir flag to dartk and test.py.

pkg/kernel/lib/text/ast_to_text.dart

Index: pkg/kernel/lib/text/ast_to_text.dart
diff --git a/pkg/kernel/lib/text/ast_to_text.dart b/pkg/kernel/lib/text/ast_to_text.dart
index 9e9a093bb2b206a8b5415e8bc8ccc4974eafb88d..18be9de8860b332563538e31d135145a2867ce16 100644
--- a/pkg/kernel/lib/text/ast_to_text.dart
+++ b/pkg/kernel/lib/text/ast_to_text.dart
@@ -92,6 +92,12 @@ String debugNodeToString(Node node) {
   return '$buffer';
 }
 
+String programToString(Program node) {
+  StringBuffer buffer = new StringBuffer();
+  new Printer(buffer, syntheticNames: new NameSystem()).writeProgramFile(node);
+  return '$buffer';
+}
+
 class NameSystem {
   final Namer<VariableDeclaration> variables =
       new Namer<VariableDeclaration>('#t');