Remove the dependency of Zone on Isolate

test/unittests/test-utils.h

Index: test/unittests/test-utils.h
diff --git a/test/unittests/test-utils.h b/test/unittests/test-utils.h
index 511e3574c869ba064c207476ac5e3b679f16a4a4..718fd5ac5977e8e6cc999418264af31de1cfb9e3 100644
--- a/test/unittests/test-utils.h
+++ b/test/unittests/test-utils.h
@@ -92,7 +92,7 @@ class TestWithIsolate : public virtual ::v8::TestWithIsolate {
 
 class TestWithZone : public TestWithIsolate {
  public:
-  TestWithZone() : zone_(isolate()) {}
+  TestWithZone() {}
   virtual ~TestWithZone();
 
   Zone* zone() { return &zone_; }