Have one, long-lived map for bound functions.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 51a7162afca577d9d1b220d69f992792bb7d856b..ae513fe40e41a500089b4ca1826cadbe84da038a 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -130,6 +130,7 @@ enum BindingFlags {
     sloppy_function_without_prototype_map) \
   V(STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX, Map, \
     strict_function_without_prototype_map) \
+  V(BOUND_FUNCTION_MAP_INDEX, Map, bound_function_map) \
   V(REGEXP_RESULT_MAP_INDEX, Map, regexp_result_map)\
   V(SLOPPY_ARGUMENTS_BOILERPLATE_INDEX, JSObject, \
     sloppy_arguments_boilerplate) \
@@ -270,6 +271,7 @@ class Context: public FixedArray {
     STRICT_FUNCTION_MAP_INDEX,
     SLOPPY_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX,
     STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX,
+    BOUND_FUNCTION_MAP_INDEX,
     INITIAL_OBJECT_PROTOTYPE_INDEX,
     INITIAL_ARRAY_PROTOTYPE_INDEX,
     BOOLEAN_FUNCTION_INDEX,