Disentangle assembler from isolate.

src/ia32/assembler-ia32.h

Index: src/ia32/assembler-ia32.h
diff --git a/src/ia32/assembler-ia32.h b/src/ia32/assembler-ia32.h
index d405a91a7d609ac42f53c3cd1d40a24132f9ddd2..e47ad086bc4b0d2636cc628f353480c68975e4d0 100644
--- a/src/ia32/assembler-ia32.h
+++ b/src/ia32/assembler-ia32.h
@@ -485,8 +485,9 @@ 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.
-  // TODO(vitalyr): the assembler does not need an isolate.
-  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
@@ -495,6 +496,7 @@ class Assembler : public AssemblerBase {
   void GetCode(CodeDesc* desc);
 
   // Read/Modify the code target in the branch/call instruction at pc.
+  // The isolate argument is unused (and may be nullptr) when skipping flushing.
   inline static Address target_address_at(Address pc, Address constant_pool);
   inline static void set_target_address_at(
       Isolate* isolate, Address pc, Address constant_pool, Address target,