[runtime] Introduce dedicated JSBoundFunction to represent bound functions.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 88ef9824f8d58c8d7ef53863395f776b3a14161f..eafdee65ab50511bd781a3b17ee7d47641460489 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -3862,6 +3862,18 @@ void MacroAssembler::AssertFunction(Register object) {
 }
 
 
+void MacroAssembler::AssertBoundFunction(Register object) {
+  if (emit_debug_code()) {
+    testb(object, Immediate(kSmiTagMask));
+    Check(not_equal, kOperandIsASmiAndNotABoundFunction);
+    Push(object);
+    CmpObjectType(object, JS_BOUND_FUNCTION_TYPE, object);
+    Pop(object);
+    Check(equal, kOperandIsNotABoundFunction);
+  }
+}
+
+
 void MacroAssembler::AssertUndefinedOrAllocationSite(Register object) {
   if (emit_debug_code()) {
     Label done_checking;