Disentangle assembler from isolate.

src/mips64/macro-assembler-mips64.cc

Index: src/mips64/macro-assembler-mips64.cc
diff --git a/src/mips64/macro-assembler-mips64.cc b/src/mips64/macro-assembler-mips64.cc
index 829293f1a0d76a96ebd164a3e5b87d8b069a840b..0bad09212fdd5def41170fcfe1b5752375347c4c 100644
--- a/src/mips64/macro-assembler-mips64.cc
+++ b/src/mips64/macro-assembler-mips64.cc
@@ -29,15 +29,16 @@ const uint32_t kSingleExponentShift = kBinary32ExponentShift;
 const uint32_t kSingleNaNShift = kSingleExponentShift - 1;
 const uint32_t kSingleNaNMask = kSingleExponentMask | (1 << kSingleNaNShift);
 
-MacroAssembler::MacroAssembler(Isolate* arg_isolate, void* buffer, int size,
+MacroAssembler::MacroAssembler(Isolate* isolate, void* buffer, int size,
                                CodeObjectRequired create_code_object)
-    : Assembler(arg_isolate, buffer, size),
+    : Assembler(isolate, buffer, size),
       generating_stub_(false),
       has_frame_(false),
-      has_double_zero_reg_set_(false) {
+      has_double_zero_reg_set_(false),
+      isolate_(isolate) {
   if (create_code_object == CodeObjectRequired::kYes) {
     code_object_ =
-        Handle<Object>::New(isolate()->heap()->undefined_value(), isolate());
+        Handle<Object>::New(isolate_->heap()->undefined_value(), isolate_);
   }
 }