Eagerly dispose of ScheduledActions.

The DOMTimer's ScheduledAction hold on to the script source and
state needed to execute the timer action. Let go of ShceduledAction's
resource early.

Apart from reducing the lifetime of script source, this is a speculative
fix for crashes reported in v8::PersistentValueVector::Clear() during
lazy sweeping of ScheduledAction objects.

R=
BUG=

Review-Url: https://codereview.chromium.org/2552673002
Cr-Commit-Position: refs/heads/master@{#436298}
5 files changed