Disentangle assembler from isolate.

src/mips64/macro-assembler-mips64.h

Index: src/mips64/macro-assembler-mips64.h
diff --git a/src/mips64/macro-assembler-mips64.h b/src/mips64/macro-assembler-mips64.h
index 0bb0ad099badea82d8b10e99c8a74b60f1a4819d..5731f6fe85aaf436a4760a46c4d082156751f049 100644
--- a/src/mips64/macro-assembler-mips64.h
+++ b/src/mips64/macro-assembler-mips64.h
@@ -170,6 +170,8 @@ class MacroAssembler: public Assembler {
   MacroAssembler(Isolate* isolate, void* buffer, int size,
                  CodeObjectRequired create_code_object);
 
+  Isolate* isolate() const { return isolate_; }
+
   // Arguments macros.
 #define COND_TYPED_ARGS Condition cond, Register r1, const Operand& r2
 #define COND_ARGS cond, r1, r2
@@ -1881,6 +1883,7 @@ const Operand& rt = Operand(zero_reg), BranchDelaySlot bd = PROTECT
   bool generating_stub_;
   bool has_frame_;
   bool has_double_zero_reg_set_;
+  Isolate* isolate_;
   // This handle will be patched with the code object on installation.
   Handle<Object> code_object_;