Remove TLS access for current Zone.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index b935ab55eab771efa4bafc54d95fba47d3ffb3f8..b9763e35ff230e91ee8a9aae410fd4aa4b0782da 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -57,7 +57,7 @@ const unsigned kNoASTId = -1;
 
 class AssemblerBase: public Malloced {
  public:
-  explicit AssemblerBase(Isolate* isolate);
+  AssemblerBase(Isolate* isolate, Zone* zone);
 
   Isolate* isolate() const { return isolate_; }
   int jit_cookie() { return jit_cookie_; }
@@ -66,9 +66,12 @@ class AssemblerBase: public Malloced {
   // cross-snapshotting.
   static void QuietNaN(HeapObject* nan) { }
 
+  Zone* zone() const { return zone_; }
+
  private:
   Isolate* isolate_;
   int jit_cookie_;
+  Zone* zone_;
 };