[turbofan] remove one level of indirection in phi inputs

src/compiler/register-allocator.h

Index: src/compiler/register-allocator.h
diff --git a/src/compiler/register-allocator.h b/src/compiler/register-allocator.h
index bd9bd55425f733c10f58081d75746fcb68e3e700..d7dd1b7358246462f2a9474399b23e23225bebd3 100644
--- a/src/compiler/register-allocator.h
+++ b/src/compiler/register-allocator.h
@@ -608,8 +608,7 @@ class RegisterAllocator FINAL : public ZoneObject {
     PhiInstruction* const phi;
     const InstructionBlock* const block;
   };
-  typedef std::map<int, PhiMapValue, std::less<int>,
-                   zone_allocator<std::pair<int, PhiMapValue>>> PhiMap;
+  typedef ZoneMap<int, PhiMapValue> PhiMap;
 
   Zone* const local_zone_;
   Frame* const frame_;