Able to reproduce the issue on Mac 10.11.6 using chrome version 55.0.2866.0 

Using the per-revision bisect providing the bisect results,
Good build: 55.0.2862.0 (Revision: 419063).
Bad build: 55.0.2863.0 (Revision: 419330).

You are probably looking for a change made after 419066 (known good), but no later than 419067 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/56eaf1eac112390d863b0d738ad97d05730d36e2..cd626f11b0ddb8fc655ac2fd808ca3930e3e29cf

From the CL above, assigning the issue to the concern owner --
@xiaochengh -- Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Thank You.

Correction in comment #0:

Manual bisect info:
Good build:55.0.2862.0 Dev
Bad build:55.0.2863.0 Dev

After locally reverting r419067 the issue no longer reproduces.

I'm going to revert r419067.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/593d84c9016da731e62991eec28d998104b121da

commit 593d84c9016da731e62991eec28d998104b121da
Author: xiaochengh <xiaochengh@chromium.org>
Date: Wed Sep 21 10:44:07 2016

Revert "Document::haveImportsLoaded() should return true when ignoring pending sheets"

This is a manual revert of commit cd626f11b0ddb8fc655ac2fd808ca3930e3e29cf
for causing  crbug.com/648547 .

It also marks editing/selection/modify_move/move_backward_line_import_crash.html
as crashing, because this layout test is a repro case of  crbug.com/646323 .

Original issue's description:
> Document::haveImportsLoaded() should return true when ignoring pending sheets
>
> BUG= 646323 
> TESTS=webkit_unit_tests DocumentLoadingRenderingTest.ShouldNotPerformRepeatedLayoutWithPendingImport DocumentLoadingRenderingTest.ShouldClearPlaceholderStyleWhenIgnoringPendingStylesheet
>
> Committed: https://crrev.com/cd626f11b0ddb8fc655ac2fd808ca3930e3e29cf
> Cr-Commit-Position: refs/heads/master@{#419067}

BUG= 648547 , 646323 
TBR=esprehn@chromium.org,rune@chromium.org

Review-Url: https://codereview.chromium.org/2353243002
Cr-Commit-Position: refs/heads/master@{#420023}

[modify] https://crrev.com/593d84c9016da731e62991eec28d998104b121da/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/593d84c9016da731e62991eec28d998104b121da/third_party/WebKit/Source/core/dom/Document.cpp
[modify] https://crrev.com/593d84c9016da731e62991eec28d998104b121da/third_party/WebKit/Source/web/tests/DocumentLoadingRenderingTest.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/62e3d20e14e91f3999e3ec92fc9f706f9b29d21b

commit 62e3d20e14e91f3999e3ec92fc9f706f9b29d21b
Author: fs <fs@opera.com>
Date: Wed Sep 21 13:48:04 2016

Widen Mac expectations for move_backward_line_import_crash.html

editing/selection/modify_move/move_backward_line_import_crash.html
appears to also Crash on Mac Debug.

https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.11%20%28dbg%29/builds/4772

TBR=xiaochengh@chromium.org
BUG= 648547 , 646323 
NOTRY=true

Review-Url: https://codereview.chromium.org/2360593002
Cr-Commit-Position: refs/heads/master@{#420040}

[modify] https://crrev.com/62e3d20e14e91f3999e3ec92fc9f706f9b29d21b/third_party/WebKit/LayoutTests/TestExpectations

r419067 is already reverted. I can no longer repro with Canary 55.0.2868.0.

Could anyone from test team help me verify if the issue is fixed?

Issue seems to be fixed as this issue no longer re-pro on Ubuntu 14.04 with Latest chrome version Dev #55.0.2868.0.

Deleted: 648547.ogv 831 KB

	648547.ogv 831 KB View Download

Can't repro either anymore.