v8::TryCatch should cancel the scheduled exception on Reset.

v8::TryCatch cancels the scheduled exception on destruction if |Rethrow|
was never called.
It is reasonable to do the same in |Reset|.

BUG=362388, 359386
LOG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/443853002

Patch from Yutaka Hirano <yhirano@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22963 ce2b1a6d-e550-0410-aec6-3dcde31c8c00