IDL compiler: EventHandler: Window.onerror, WorkerGlobalScope.onerror

Remaining: 5 => 4

BUG=239771
R=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/141703027

git-svn-id: svn://svn.chromium.org/blink/trunk@166471 bbb929c8-8fbe-4397-9dbb-9b2b20218538