First steps towards better code generation for LBranch:

src/ast.h

Index: src/ast.h
===================================================================
--- src/ast.h	(revision 8228)
+++ src/ast.h	(working copy)
@@ -210,7 +210,7 @@
     kTest
   };
 
-  Expression() : id_(GetNextId()) {}
+  Expression() : id_(GetNextId()), test_id_(GetNextId()) {}
 
   virtual int position() const {
     UNREACHABLE();
@@ -269,10 +269,12 @@
   }
 
   unsigned id() const { return id_; }
+  unsigned test_id() const { return test_id_; }
 
  private:
   ExternalArrayType external_array_type_;
   unsigned id_;
+  unsigned test_id_;
 };