Revert "Remove ContrastAdjust()."

This reverts commit 53d443f042b590ae2d920def16bc9daf66f8427d.

Reason for revert: Breaks PDFToPWGRasterBrowserTest

Original change's description:
> Remove ContrastAdjust().
> 
> This post-processing increased the contrast of scaled-down features -
> mainly lines and fonts, relative to the background. The effect does not
> improved readability and in some cases makes the scaled-down version
> look like a different document at a glance. Text that is normal
> weight appears bold when scaled down in these cases.
> 
> Change-Id: I2544d45e2bcec25d6742d2a60c1316d8df08cce1
> Reviewed-on: https://pdfium-review.googlesource.com/15471
> Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
> Reviewed-by: dsinclair <dsinclair@chromium.org>

TBR=bungeman@chromium.org,dsinclair@chromium.org,hnakashima@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I7f61650bc6d917b3c6640da60f3f740ef4498de0
Reviewed-on: https://pdfium-review.googlesource.com/16970
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>

1 files changed, 0 insertions, 0 deletions

diff --git a/testing/resources/pixel/font_size_expected.pdf.0.png b/testing/resources/pixel/font_size_expected.pdf.0.png
index b4506e0d2c..bcb30c4cb6 100644
--- a/testing/resources/pixel/font_size_expected.pdf.0.png
+++ b/testing/resources/pixel/font_size_expected.pdf.0.png