Just so I'm understanding this correctly: If you drag white text on a black background, the text is readable?

The drag image gets created in blink, so it would have to know beforehand, somehow, if transparency is available.

The drag and drop window is supposed to be transparent. But without a compositing manager that window will have a black background. The background color of the page doesn't really matter.

My CL to fix this: https://chromium-review.googlesource.com/c/481103/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4dc0ad690ed3a08c56b78b0f679580f74d3acf73

commit 4dc0ad690ed3a08c56b78b0f679580f74d3acf73
Author: Sunny Sachanandani <sunnyps@chromium.org>
Date: Fri Apr 21 22:32:40 2017

x11: Use opaque window for dnd without composite.

Use an opaque window for drag and drop when a compositing manager is
absent. Otherwise, the drag and drop window is displayed black.

BUG= 712896 

Change-Id: I753cc26f5713579e3fc6ffbd952c62ee44d9ae44
Reviewed-on: https://chromium-review.googlesource.com/481103
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Elliot Glaysher <erg@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#466468}
[modify] https://crrev.com/4dc0ad690ed3a08c56b78b0f679580f74d3acf73/content/browser/gpu/gpu_internals_ui.cc
[modify] https://crrev.com/4dc0ad690ed3a08c56b78b0f679580f74d3acf73/ui/base/x/x11_util.cc
[modify] https://crrev.com/4dc0ad690ed3a08c56b78b0f679580f74d3acf73/ui/base/x/x11_util.h
[modify] https://crrev.com/4dc0ad690ed3a08c56b78b0f679580f74d3acf73/ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc

Your change meets the bar and is auto-approved for M59. Please go ahead and merge the CL to branch 3071 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), gkihumba@(ChromeOS), Abdul Syed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c3cfef7a2bafdb9753d97e01f544f9ab2083bc3c

commit c3cfef7a2bafdb9753d97e01f544f9ab2083bc3c
Author: Sunny Sachanandani <sunnyps@chromium.org>
Date: Mon Apr 24 21:13:43 2017

x11: Use opaque window for dnd without composite.

Use an opaque window for drag and drop when a compositing manager is
absent. Otherwise, the drag and drop window is displayed black.

BUG= 712896 

Change-Id: I753cc26f5713579e3fc6ffbd952c62ee44d9ae44
Reviewed-on: https://chromium-review.googlesource.com/481103
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Elliot Glaysher <erg@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#466468}(cherry picked from commit 4dc0ad690ed3a08c56b78b0f679580f74d3acf73)
Review-Url: https://codereview.chromium.org/2838753002 .
Cr-Commit-Position: refs/branch-heads/3071@{#179}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/c3cfef7a2bafdb9753d97e01f544f9ab2083bc3c/content/browser/gpu/gpu_internals_ui.cc
[modify] https://crrev.com/c3cfef7a2bafdb9753d97e01f544f9ab2083bc3c/ui/base/x/x11_util.cc
[modify] https://crrev.com/c3cfef7a2bafdb9753d97e01f544f9ab2083bc3c/ui/base/x/x11_util.h
[modify] https://crrev.com/c3cfef7a2bafdb9753d97e01f544f9ab2083bc3c/ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc