Disentangle assembler from isolate.

src/x87/assembler-x87.h

Index: src/x87/assembler-x87.h
diff --git a/src/x87/assembler-x87.h b/src/x87/assembler-x87.h
index c2105be9417e95494a556529e5d824521cdbf273..8b9cda4357916c57d6a2e7b69763fe5ed76521a9 100644
--- a/src/x87/assembler-x87.h
+++ b/src/x87/assembler-x87.h
@@ -483,8 +483,9 @@ 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
@@ -493,6 +494,7 @@ 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,