I think we have two problems here.

Problem 1: The inline margin is ignored. It should have been enough to trigger creation of a line
Problem 2: We create a line from whitespace that should really be ignored (but I really don't know those rules)

Attaching a test case for problem 2, with plenty of whitespace - none of which should trigger line creation or give the containing block any height. This is what makes external/wpt/css/CSS2/floats-clear/floats-149.xht pass, as long as we don't remove too much unnecessary whitespace LayoutObjects.

Deleted: no-meaningful-whitespace.html 249 bytes

no-meaningful-whitespace.html 249 bytes View Download

Thank you for the attention. Inline margin in LayoutNG was supported a few days ago, and I'm making the condition more strict in https://codereview.chromium.org/2931363002. I don't have build right now but inline margin should be working, I'll check later. I guess it should be working in ToT but if not, the WIP CL should fix.

For the whitespace rule, yeah, I found some code in the current code saying sometimes the current code creates lines from whitespaces and sometimes don't, but I haven't figured them out yet.

If this is blocking, please feel free to mark as Failure in TestExpectations. We're looking at all those failures and trying to fix them. In some aspects, LayoutNG passes where the current layout code fails, but in most cases LayoutNG needs to be better.

The WIP is under review now, it passes Rune's test, but not Morten's yet. It's on my backlog.

Forgot to mark this bug but the CL fixed Rune's test.
https://codereview.chromium.org/2931363002

For Morten's, I found I misunderstood it at the first time, now I understand. This is a separate issue, about white space collapsing, and NG isn't collapsing the space when it should. I double checked the current BreakingContext and understood what NG should do.

Not sure if we have tests for this in LayoutTests or wpt, I'll check.

Confirmed test #1 is whitespace collapsing issue that was on my back log for 3 months and I was almost forgotten, thank you for this! WIP:
https://codereview.chromium.org/2951213005

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165

commit 0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165
Author: kojii <kojii@chromium.org>
Date: Sat Jun 24 17:20:23 2017

[LayoutNG] Support objects that are opaque to whitespace collapsing

This patch changes following objects opaque to whitespace collapsing;
i.e., spaces before such objects and after can collapse.
- Out-of-flow objects (floats, absolute positioned objects.)
- Open/close tags.
- Bidi controls.

The ability (AppendAsOpaqueToSpaceCollapsing) originally existed and
used for bidi controls, but removed in [1] due to lack of spec and
tests. Above cases were tested in 4 browsers and re-implemented to be
interoperable.

This patch also stops injecting Object Replacement Character for OOF
objects. This is not specified, and was not possible before, but
0-length item was supported for open/close tags, and this behavior is
interopeable with Blink/Edge/WebKit.

[1] https://codereview.chromium.org/2749013003

BUG=636993,  733609 

Review-Url: https://codereview.chromium.org/2951213005
Cr-Commit-Position: refs/heads/master@{#482152}

[modify] https://crrev.com/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165/third_party/WebKit/LayoutTests/virtual/layout_ng/fast/block/float/overhanging-float-crashes-when-sibling-becomes-formatting-context-expected.txt
[add] https://crrev.com/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165/third_party/WebKit/LayoutTests/virtual/layout_ng/fast/block/float/selection-gap-clip-out-tiger-crash-expected.txt
[delete] https://crrev.com/b2543b5d009a924286be4144384890f82d8cc180/third_party/WebKit/LayoutTests/virtual/layout_ng/fast/block/margin-collapse/self-collapsing-block-discards-margin-expected.txt
[modify] https://crrev.com/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_items_builder.cc
[modify] https://crrev.com/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_items_builder.h
[modify] https://crrev.com/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_items_builder_test.cc
[modify] https://crrev.com/0a3ecc6715b7ad1c10bc6b4384d0bad5c8e0d165/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_node.cc

Thank you both for the help!