[Binding] use V8TRYCATCH_VOID and raw pointer in indexed setter

We use V8TRYCATCH_VOID when we assign converted JS value
into native variable, and the native variable type is
raw pointer if the type is not primitive.
(occur in attribute setter and function)

However, in generated indexed setter
they are simple assignment without try-catch and variable type is RefPtr.

This patch unify the situation by using V8TRYCATCH_VOID and raw pointer.

R=haraken@chromium.org
BUG=239771
TEST=TestEventTarget.idl

Review URL: https://chromiumcodereview.appspot.com/18677002

git-svn-id: svn://svn.chromium.org/blink/trunk@153567 bbb929c8-8fbe-4397-9dbb-9b2b20218538