Improve handling of property loads on the proto chain.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 43fb8b9ba0de5474ce8f3de5c3cd9a4fb117531e..0b91e2f3e93f29908d6408d3346956eb6bfaffee 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1667,9 +1667,9 @@ LInstruction* LChunkBuilder::DoCheckInstanceType(HCheckInstanceType* instr) {
 
 
 LInstruction* LChunkBuilder::DoCheckPrototypeMaps(HCheckPrototypeMaps* instr) {
-  LOperand* temp = TempRegister();
+  LUnallocated* temp = TempRegister();
   LCheckPrototypeMaps* result = new(zone()) LCheckPrototypeMaps(temp);
-  return AssignEnvironment(result);
+  return AssignEnvironment(Define(result, temp));
 }