Fix BUILD.gn

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/442343003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22937 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Add `CheckObjectCoercible` for the `String.prototype` HTML methods

Contributed by Mathias Bynens <mathiasb@opera.com>.

TEST=mjsunit/es6/string-html
BUG=v8:2218
LOG=Y
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/422543003

Patch from Mathias Bynens <mathias@qiwi.be>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00