Fix thumbnail load detection on Webkit

Authored by matthiasmullie on Tue, Feb 13, 1:52 PM.

Description

Fix thumbnail load detection on Webkit

Unfortunately, Webkit has a longstanding bug
(https://bugs.chromium.org/p/chromium/issues/detail?id=7731)
where load events are not triggered when the source of an
image gets set to the same thing it was already.

There is a workaround: construct a separate Image object
where you load that same source, and let the one trigger the
event...

Bug: T187192
Change-Id: Ifbe141136842933c46f9b6cd9313b8b6dc92ec59
(cherry picked from commit 8b933c0e08c6577f99022df3002f2ec04f24eefa)