And the original bug reporter is correct. The issue is in PDFium. On Windows, one can run pdfium_test --emf imagemask.pdf, and the output .emf file has red text.

And since it's EMF, we need to talk to win32. In this case, we call CreateSolidBrush() with a COLORREF. COLORREFs are BGR, but since they are really just DWORDs underneath, it's really easy to assign another unsigned int into it. In this case, the input is RGB. So there ya go.

https://pdfium-review.googlesource.com/28573

The following revision refers to this bug:
  https://pdfium.googlesource.com/pdfium/+/0202adeb5a042ca43f29439ef59e7bc3d4f8268f

commit 0202adeb5a042ca43f29439ef59e7bc3d4f8268f
Author: Lei Zhang <thestig@chromium.org>
Date: Thu Mar 15 14:59:47 2018

Fix a red-blue channel flip when rendering masks to EMF.

Use BGR instead of RGB in CGdiDeviceDriver::GDI_StretchBitMask(). Many
win32 GDI APIs take COLORREF as input, and COLORREF is BGR. In this
case, a win32 API was being called with RGB data.

BUG= chromium:821672 

Change-Id: Ia530c7ef5582eed13ac7119935851cfe0ad57323
Reviewed-on: https://pdfium-review.googlesource.com/28573
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>

[modify] https://crrev.com/0202adeb5a042ca43f29439ef59e7bc3d4f8268f/core/fxge/win32/fx_win32_device.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3389b74210104fb6d3a82df85cf7c121d0c2fcf6

commit 3389b74210104fb6d3a82df85cf7c121d0c2fcf6
Author: pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Date: Thu Mar 15 22:12:48 2018

Roll src/third_party/pdfium/ d1ffda2ac..35841fa4e (6 commits)

https://pdfium.googlesource.com/pdfium.git/+log/d1ffda2acaee..35841fa4e3db

$ git log d1ffda2ac..35841fa4e --date=short --no-merges --format='%ad %ae %s'
2018-03-15 hnakashima Create FPDFPage_RemoveObject().
2018-03-15 rharrison Fixing order of guards to avoid potential segvs
2018-03-15 thestig Rename FX_COLORREF variables from "rgb" to "bgr".
2018-03-15 thestig Use Width()/Height() methods from rectangles.
2018-03-15 thestig Remove unused CPDFSDK_BAAnnot methods.
2018-03-15 thestig Fix a red-blue channel flip when rendering masks to EMF.

Created with:
  roll-dep src/third_party/pdfium
BUG= 821672 


The AutoRoll server is located here: https://pdfium-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


TBR=dsinclair@chromium.org

Change-Id: If141edae0fe9d00e024a14545336834d172420e9
Reviewed-on: https://chromium-review.googlesource.com/964620
Commit-Queue: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Reviewed-by: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#543513}
[modify] https://crrev.com/3389b74210104fb6d3a82df85cf7c121d0c2fcf6/DEPS