[builtins] Start refactoring the Apply builtin.

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 471fa55cb0a02ec189669a845cb96b79de6ab9c2..d979d496936974500bed47a901a60c04aef810f1 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -3701,6 +3701,16 @@ void MacroAssembler::AssertSmi(const Operand& object) {
   }
 }
 
+void MacroAssembler::AssertFixedArray(Register object) {
+  if (emit_debug_code()) {
+    testb(object, Immediate(kSmiTagMask));
+    Check(not_equal, kOperandIsASmiAndNotAFixedArray);
+    Push(object);
+    CmpObjectType(object, FIXED_ARRAY_TYPE, object);
+    Pop(object);
+    Check(equal, kOperandIsNotAFixedArray);
+  }
+}
 
 void MacroAssembler::AssertZeroExtended(Register int32_register) {
   if (emit_debug_code()) {