Rewrite image URLs for preprocess=true.

We did this by default and for flattenhtml=true, but not when setting
preprocess=true.  This seems like an oversight.

Bug: 564112
Change-Id: Id3d6907e79be51ea2ce905e563f350fd0f882164
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1670353
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672120}
2 files changed