Bisected to https://chromium.googlesource.com/chromium/src/+log/540399d5f34abfcae1828e2c36835ffae391e319..d748f22c6fa57ce44370686d816500f8cc9cb2aa.

Suspecting https://chromium.googlesource.com/chromium/src/+/2ef7df4c03595db39c1b0c303ec8a822f0bf30c9.

@trchen can you take a look?

More about the test:
- Please see the attached screenshot for good (need to scroll to the bottom of the page) and bad behavior.
- The issue can be reproduced on all high-dpi devices and low-dpi devices with --enable-prefer-compositing-to-lcd-text.
- On low-dpi devices without --enable-prefer-compositing-to-lcd-text, the test is not stable. Sometimes it shows good sometimes bad and sometimes it flashes between good and bad.

Deleted: good.png 306 KB

	good.png 306 KB View Download

Deleted: bad.png 537 KB

	bad.png 537 KB View Download

Based on the CL, it seems that it's a correct behavior that the fixed-position child escapes overflow clip of the absolute parent. I'm marking this bug WontFix.

@trchen please confirm.

Firefox also behaves the same as us.

> - On low-dpi devices without --enable-prefer-compositing-to-lcd-text, the test is not stable...

Never mind the above statement. trchen's change actually fixed the unstable behavior on low-dpi devices.

The page can achieve the same effect using the following:

<div style="position: absolute; top: 500px; left: 10px; width: 100px; height: 100px;
   background-image: linear-gradient(blue, red); /* the image */
   background-attachment: fixed;"></div>
<div style="height: 4000px"></div>