Revert of Fix ImageLoader::m_hasPendingLoadEvent/m_imageComplete in ImageDocument (patchset #4 id:60001 of https://codereview.chromium.org/2208073004/ )

Reason for revert:
Reverting since http/tests/images/png-partial-load-as-document.html consistently leaks on WebKit Linux Leak and LeakExpectations says "Sheriff is expected to revert culprit CLs instead of suppressing the leaks"

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=http%2Ftests%2Fimages%2Fpng-partial-load-as-document.html&testType=webkit_tests

Original issue's description:
> Fix ImageLoader::m_hasPendingLoadEvent/m_imageComplete in ImageDocument
>
> Case 1: When a image is loaded as a subresource, loading is stared by
> ImageResource::fetch() in ImageLoader::doUpdateFromElement().
> Case 2: When a image is loaded as a main document, the start of the loading is
> emulated by setImage() in ImageLoader::updateFromElement() and
> ImageDocumentParser will do the subsequent loading steps.
>
> However in Case 2, |m_hasPendingLoadEvent| is set to false
> (in setImageWithoutConsideringPendingLoadEvent()), causing |imageStillLoading|
> to be false and ensureFallbackContent() to be called in
> HTMLImageElement::selectSourceURL(), and thus a box indicating a broken image
> is displayed during loading instead of the image displayed progressively.
> This is regression since https://codereview.chromium.org/1879793003.
>
> This CL makes the behavior of Case 1 and 2 consistent, by moving what is done
> in Case 1 to setImagePending(), and makes Case 1 and 2 both to call
> setImagePending().
>
> This CL also adds a layout test to confirm that an image is displayed
> progressively when loaded as a main document.
>
> BUG=632495
>
> Committed: https://crrev.com/576c7a048bfc30faf510eeda07f303fa9dd12898
> Cr-Commit-Position: refs/heads/master@{#414008}

TBR=japhet@chromium.org,yhirano@chromium.org,hiroshige@chromium.org
NOTRY=true
NOTREECHECKS=true
BUG=632495

Review-Url: https://codereview.chromium.org/2278953002
Cr-Commit-Position: refs/heads/master@{#414441}
5 files changed