Disentangle assembler from isolate.

src/mips/assembler-mips.h

Index: src/mips/assembler-mips.h
diff --git a/src/mips/assembler-mips.h b/src/mips/assembler-mips.h
index 2018fc8a853f3de9f71d6b309fe861638954226b..1eb853810c76f7d3de412d86870c58331e572c7a 100644
--- a/src/mips/assembler-mips.h
+++ b/src/mips/assembler-mips.h
@@ -384,7 +384,9 @@ class Assembler : public AssemblerBase {
   // for code generation and assumes its size to be buffer_size. If the buffer
   // is too small, a fatal error occurs. No deallocation of the buffer is done
   // upon destruction of the assembler.
-  Assembler(Isolate* isolate, void* buffer, int buffer_size);
+  Assembler(Isolate* isolate, void* buffer, int buffer_size)
+      : Assembler(IsolateData(isolate), buffer, buffer_size) {}
+  Assembler(IsolateData isolate_data, void* buffer, int buffer_size);
   virtual ~Assembler() { }
 
   // GetCode emits any pending (non-emitted) code and fills the descriptor
@@ -455,6 +457,7 @@ class Assembler : public AssemblerBase {
   void label_at_put(Label* L, int at_offset);
 
   // Read/Modify the code target address in the branch/call instruction at pc.
+  // The isolate argument is unused (and may be nullptr) when skipping flushing.
   static Address target_address_at(Address pc);
   static void set_target_address_at(
       Isolate* isolate, Address pc, Address target,