Improve handling of property loads on the proto chain.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 374e54c97389e448721421ca80898aeb6d42df1d..f72fd87ce60ab5bd49ed5318c5b39931a6dc009c 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -6030,6 +6030,19 @@ HInstruction* HGraphBuilder::BuildLoadNamedMonomorphic(HValue* object,
     return new(zone()) HConstant(function, Representation::Tagged());
   }
 
+  // Handle a load from a known field somewhere in the protoype chain.
+  LookupInPrototypes(map, name, &lookup);
+  if (lookup.IsField()) {
+    Handle<JSObject> prototype(JSObject::cast(map->prototype()));
+    Handle<JSObject> holder(lookup.holder());
+    Handle<Map> holder_map(holder->map());
+    AddInstruction(new(zone()) HCheckNonSmi(object));
+    AddInstruction(HCheckMaps::NewWithTransitions(object, map, zone()));
+    HInstruction* holder_value =
+        AddInstruction(new(zone()) HCheckPrototypeMaps(prototype, holder));
+    return BuildLoadNamedField(holder_value, holder_map, &lookup, false);
+  }
+
   // No luck, do a generic load.
   return BuildLoadNamedGeneric(object, name, expr);
 }