Disentangle assembler from isolate.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index 3226d9373f601039bde0d9cf0528953f143a1b03..f5fdff51acf0e20fa89b7d0cc6596c350f15000e 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -18,15 +18,16 @@
 namespace v8 {
 namespace internal {
 
-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_);
   }
 }