Fix InstallPhaseEvent so that instances can be passed to script.

Events need to provide the V8Event binding their interface name (by
overriding Event::interfaceName) and set up wrapper info (by calling
ScriptWrappable::init.) Make InstallPhaseEvent follow the rules.

BUG=356021

Review URL: https://codereview.chromium.org/216603003

git-svn-id: svn://svn.chromium.org/blink/trunk@170322 bbb929c8-8fbe-4397-9dbb-9b2b20218538