Fix leak in cctest/test-heap/ReleaseStackTraceData

TBR=svenpanne@chromium.org
BUG=none
LOG=n

Review URL: https://codereview.chromium.org/585843002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24068 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/cctest/test-heap.cc

@@ -3387,6 +3387,7 @@ UNINITIALIZED_TEST(ReleaseStackTraceData) {
     ReleaseStackTraceDataTest(isolate, source3, getter);
     ReleaseStackTraceDataTest(isolate, source4, getter);
   }
+  isolate->Dispose();
 }