Use wrapper tracing in ErrorEvent

Having ScriptValue in ErrorEvent creates a cycle reference between
blink and v8 and causes memory leak. Fix it by using wrapper tracing.

BUG=701695,501866

Change-Id: I3235bc52f95e9fb54ab37e234269ffe5374f10c6
Reviewed-on: https://chromium-review.googlesource.com/527547
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478546}
5 files changed