Revert of Load data URI images in an async way according to spec (patchset #2 id:20001 of https://codereview.chromium.org/1492303003/ )

Reason for revert:
Perf regressions: https://code.google.com/p/chromium/issues/detail?id=569023

Original issue's description:
> Load data URI images in an async way according to spec
>
> According to https://github.com/ResponsiveImagesCG/picture-element/issues/223#issuecomment-69772765
> we seem to be the only browser that loads data URIs immediately (as if they were cached).
> It was introduced as part of the move to async image loading: https://codereview.chromium.org/200923002
>
> This is now causing issues: https://code.google.com/p/chromium/issues/detail?id=469131
>
> This CL changes this behavior to be spec compliant and load data URIs asynchronously, like other resources.
>
> This is bringing https://codereview.chromium.org/1256233002/ to the Chromium repo.
>
> BUG=514206
>
> Committed: https://crrev.com/91aa6fb579a1f656ef274ebe73e426db99b5f52f
> Cr-Commit-Position: refs/heads/master@{#363444}

TBR=pdr@chromium.org,mkwst@chromium.org,esprehn@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=514206

Review URL: https://codereview.chromium.org/1525793006

Cr-Commit-Position: refs/heads/master@{#365498}
15 files changed