Fix issue with getOwnPropertySymbols and hidden properties

When getting the symbols of an object we need to ignore the hidden
properties of the prototype object since the hidden properties are
represented by a single string key and we will not include that hidden
string in the found names.

BUG=350864
LOG=Y
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/192883005

Patch from Erik Arvidsson <arv@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19813 ce2b1a6d-e550-0410-aec6-3dcde31c8c00