pdr@, any reason this is under Blink>Scroll? Did you mean to set Blink>Animation (Since it's from UpdateAnimations())?

No reason, animation sounds good to me.

\i. DocumentAnimations::UpdateAnimations has a DCHECK at the start that the current lifecycle state is at least the one passed in by the caller.
ii. LocalFrameView::UpdateLifecyclePhasesInternal for BlinkGenPropertyTrees calls the update here: https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/frame/local_frame_view.cc?type=cs&sq=package:chromium&g=0&l=3308 with kPaintClean as the required state.

iii. However for this test, the current lifecycle is actually kPrePaintClean before the call:

[249813:249813:0518/133313.023891:2175096848784:INFO:local_frame_view.cc(3315)] Before DocumentAnimations::UpdateAnimations call, state is 15

pdr@ - what is the expected lifecycle at that point in UpdateLifecyclePhasesInternal for BlinkGenPropertyTrees? If kPrePaintClean is a valid state, we need to determine if that's ok for animations (what might be missing, etc), and perhaps move the UpdateAnimations call to when things are definitely safe.

This is because printing skips paint at this line:

https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/frame/local_frame_view.cc?type=cs&sq=package:chromium&g=0&l=3298

The same conditional should be added to the animations code below.

Ack, I can fix that.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c56f92254ed07045e6a0175bde6efe9dfe8635a6

commit c56f92254ed07045e6a0175bde6efe9dfe8635a6
Author: Stephen McGruer <smcgruer@chromium.org>
Date: Tue May 22 22:27:45 2018

Don't call DocumentAnimations::UpdateAnimations when in print mode

When in print mode, we don't do 'normal' visual output; painting is done
explicitly to a special output canvas. As such, there is little point in
doing composited animation updates, as we will not be showing the result.

This also fixes a DCHECK in BlinkGenPropertyTrees/SPv2 mode, where paint
was skipped but DocumentAnimations::UpdateAnimations wasn't - this caused
UpdateAnimations to fail its DCHECK for the expected lifecycle state.

Bug:  842937 
Cq-Include-Trybots: luci.chromium.try:linux-blink-gen-property-trees;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: If8a0e11bd25e931dd02434e18ec90a02c4e8f9e1
Reviewed-on: https://chromium-review.googlesource.com/1066405
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560815}
[modify] https://crrev.com/c56f92254ed07045e6a0175bde6efe9dfe8635a6/third_party/blink/renderer/core/frame/local_frame_view.cc
[modify] https://crrev.com/c56f92254ed07045e6a0175bde6efe9dfe8635a6/third_party/blink/renderer/core/page/print_context_test.cc
[modify] https://crrev.com/c56f92254ed07045e6a0175bde6efe9dfe8635a6/third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc