Use auto-rethrowing v8::TryCatch variant

To avoid the need to call ReThrow() on the v8::TryCatch that may or
may not be declared, and the risk of forgetting to do so in some case,
use an auto-rethrowing v8::TryCatch variant instead.

BUG=362388

Review URL: https://codereview.chromium.org/304223007

git-svn-id: svn://svn.chromium.org/blink/trunk@175134 bbb929c8-8fbe-4397-9dbb-9b2b20218538