Remove TLS access for current Zone.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 05fe320ad013f929c2a723dc9bd0ea2b35c62ade..bd382171e58860949a2c6aecc5a9bcfc1d7d51e4 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() { return zone_; }
+
  private:
   Isolate* isolate_;
   int jit_cookie_;
+  Zone* zone_;
 };