Make HCheckPrototypeMaps compatible with parallel recompilation.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index 138bee04de4677d8178ae359c852f27a1a965724..70526c15b58af23c9412106f4e4a6fa9acf4716c 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -1193,7 +1193,8 @@ void HCheckInstanceType::PrintDataTo(StringStream* stream) {
 
 
 void HCheckPrototypeMaps::PrintDataTo(StringStream* stream) {
-  stream->Add("[receiver_prototype=%p,holder=%p]", *prototype(), *holder());
+  stream->Add("[receiver_prototype=%p,holder=%p]",
+              *prototypes_.first(), *prototypes_.last());
 }