[runtime] Introduce dedicated JSBoundFunction to represent bound functions.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 822654201129df645429fbde246c5aac53172a89..6f09236a3cf3e9960e150034916013488c317453 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1215,6 +1215,10 @@ class MacroAssembler: public Assembler {
   // Abort execution if argument is not a JSFunction, enabled via --debug-code.
   void AssertFunction(Register object);
 
+  // Abort execution if argument is not a JSBoundFunction,
+  // enabled via --debug-code.
+  void AssertBoundFunction(Register object);
+
   // Abort execution if argument is not undefined or an AllocationSite, enabled
   // via --debug-code.
   void AssertUndefinedOrAllocationSite(Register object);