remove remaining uses of default isolate in tests

test/cctest/cctest.h

Index: test/cctest/cctest.h
diff --git a/test/cctest/cctest.h b/test/cctest/cctest.h
index 122d36d5b8383fb30abbcb4fbb359f22ebfc21fb..b9c5d00fdd15cf979fb682a98683710d3815a890 100644
--- a/test/cctest/cctest.h
+++ b/test/cctest/cctest.h
@@ -93,6 +93,7 @@ class CcTest {
   bool enabled() { return enabled_; }
 
   static v8::Isolate* isolate() {
+    CHECK(isolate_ != NULL);
     isolate_used_ = true;
     return isolate_;
   }
@@ -115,6 +116,9 @@ class CcTest {
     v8::Context::New(CcTest::isolate())->Enter();
   }
 
+  // Only for UNINITIALIZED_TESTs
+  static void DisableAutomaticDispose();
+
   // Helper function to configure a context.
   // Must be in a HandleScope.
   static v8::Local<v8::Context> NewContext(