Additional minor cleanup regarding CallWrapper: Use the null object pattern.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
===================================================================
--- src/mips/macro-assembler-mips.cc	(revision 7766)
+++ src/mips/macro-assembler-mips.cc	(working copy)
@@ -2255,7 +2255,7 @@
                                     Register code_reg,
                                     Label* done,
                                     InvokeFlag flag,
-                                    CallWrapper* call_wrapper) {
+                                    const CallWrapper& call_wrapper) {
   bool definitely_matches = false;
   Label regular_invoke;
 
@@ -2308,11 +2308,9 @@
     Handle<Code> adaptor =
         isolate()->builtins()->ArgumentsAdaptorTrampoline();
     if (flag == CALL_FUNCTION) {
-      if (call_wrapper != NULL) {
-        call_wrapper->BeforeCall(CallSize(adaptor, RelocInfo::CODE_TARGET));
-      }
+      call_wrapper.BeforeCall(CallSize(adaptor, RelocInfo::CODE_TARGET));
       Call(adaptor, RelocInfo::CODE_TARGET);
-      if (call_wrapper != NULL) call_wrapper->AfterCall();
+      call_wrapper.AfterCall();
       jmp(done);
     } else {
       Jump(adaptor, RelocInfo::CODE_TARGET);
@@ -2326,7 +2324,7 @@
                                 const ParameterCount& expected,
                                 const ParameterCount& actual,
                                 InvokeFlag flag,
-                                CallWrapper* call_wrapper) {
+                                const CallWrapper& call_wrapper) {
   Label done;
 
   InvokePrologue(expected, actual, Handle<Code>::null(), code, &done, flag,
@@ -2365,7 +2363,7 @@
 void MacroAssembler::InvokeFunction(Register function,
                                     const ParameterCount& actual,
                                     InvokeFlag flag,
-                                    CallWrapper* call_wrapper) {
+                                    const CallWrapper& call_wrapper) {
   // Contract with called JS functions requires that function is passed in a1.
   ASSERT(function.is(a1));
   Register expected_reg = a2;
@@ -2657,12 +2655,12 @@
 
 void MacroAssembler::InvokeBuiltin(Builtins::JavaScript id,
                                    InvokeFlag flag,
-                                   CallWrapper* call_wrapper) {
+                                   const CallWrapper& call_wrapper) {
   GetBuiltinEntry(t9, id);
   if (flag == CALL_FUNCTION) {
-    if (call_wrapper != NULL) call_wrapper->BeforeCall(CallSize(t9));
+    call_wrapper.BeforeCall(CallSize(t9));
     Call(t9);
-    if (call_wrapper != NULL) call_wrapper->AfterCall();
+    call_wrapper.AfterCall();
   } else {
     ASSERT(flag == JUMP_FUNCTION);
     Jump(t9);