Reland of HTMLImageElement: do not use fallback content for ImageDocument (patchset #1 id:1 of https://codereview.chromium.org/2365523003/ )

Reason for revert:
As per comment #8, this CL wasn't the cause of bot failures.
https://codereview.chromium.org/2365523003/#msg8

Original issue's description:
> Revert of HTMLImageElement: do not use fallback content for ImageDocument (patchset #2 id:20001 of https://codereview.chromium.org/2343613002/ )
>
> Reason for revert:
> Speculatively reverting to fix broken layout tests on Windows (https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Win10, https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Win7)
>
> Tests are
>
> fast/backgrounds/border-radius-split-background-image.html
> fast/backgrounds/border-radius-split-background.html
> fast/borders/border-styles-split.html
> paint/invalidation/background-resize-height.html
>
> Original issue's description:
> > HTMLImageElement: do not use fallback content for ImageDocument
> >
> > After https://codereview.chromium.org/1879793003,
> > ImageLoader::hasPendingActivity() became false for ImageDocument and thus
> > HTMLImageElement::selectSourceURL() didn't consider the image as still loading
> > during load (|imageStillLoading| became false).
> > This caused ImageDocument not to be displayed progressively.
> >
> > This CL makes HTMLImageElement to use primary content for ImageDocument.
> > This causes ImageDocument not to be replaced with fallback content, but I
> > expect that is more acceptable than images not displayed progressively.
> >
> > BUG=632495
> >
> > Committed: https://crrev.com/c5e43f7edf4e55155fcda51be0285f37b20c2e76
> > Cr-Commit-Position: refs/heads/master@{#420432}
>
> TBR=yhirano@chromium.org,japhet@chromium.org,ellyjones@chromium.org,hiroshige@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=632495
>
> Committed: https://crrev.com/70e44d10fc52150a6af5a7de760cb9181587fbb4
> Cr-Commit-Position: refs/heads/master@{#420499}

TBR=yhirano@chromium.org,japhet@chromium.org,ellyjones@chromium.org,gcasto@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=632495

Review-Url: https://codereview.chromium.org/2364073002
Cr-Commit-Position: refs/heads/master@{#420616}
5 files changed