There are some differences right now between the flags used in Chromium for Android and what DumpRenderTree gets passed for running layout tests. For the most accurate results, these should be synchronized as much as possible. When we switch to using content_shell as the test runner, this should also become much easier to keep in sync..
I was planning to add two flags: --force-composited-mode and --enable-accelerated-fixed-position (new flag). We'd also need --enable-threaded-compositing but current it crashes the test runner.
Resolving as WontFix given that Chromium moved to Blink.