I will take this.
A Patch has submitted:
https://chromium-review.googlesource.com/c/chromium/src/+/936941

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7af65ec1c9625fb6058ca79a8df56147359f2308

commit 7af65ec1c9625fb6058ca79a8df56147359f2308
Author: Zhuoyu Qian <zhuoyu.qian@samsung.com>
Date: Mon Feb 26 03:16:08 2018

[css-typed-om] StylePropertyMapOnly.size changed to unsigned

StylePropertyMapOnly.size should be unsigned:
https://github.com/w3c/css-houdini-drafts/commit/2da28139b2f817e241fc55a35f8c4b2825835308

Bug:  815040 

Signed-off-by: Zhuoyu Qian <zhuoyu.qian@samsung.com>
Change-Id: Ib72d13ab5ee90936ca54829fd1f230223ddef7b5
Reviewed-on: https://chromium-review.googlesource.com/936941
Reviewed-by: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539062}
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/ComputedStylePropertyMap.cpp
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/ComputedStylePropertyMap.h
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/DeclaredStylePropertyMap.cpp
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/DeclaredStylePropertyMap.h
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/FilteredComputedStylePropertyMap.cpp
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/FilteredComputedStylePropertyMap.h
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/InlineStylePropertyMap.cpp
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/InlineStylePropertyMap.h
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/StylePropertyMapReadOnly.h
[modify] https://crrev.com/7af65ec1c9625fb6058ca79a8df56147359f2308/third_party/WebKit/Source/core/css/cssom/StylePropertyMapReadOnly.idl