Thomas looked into this and found the log contains references to CSS things being dirty:
...
ninja explain: obj/third_party/WebKit/Source/core/make_core_generated_css_longhand_property_apis.stamp is dirty
ninja explain: obj/third_party/WebKit/Source/core/make_core_generated_css_shorthand_property_apis.stamp is dirty
ninja explain: obj/tools/v8_context_snapshot/generate_v8_context_snapshot.stamp is dirty
ninja explain: obj/third_party/WebKit/Source/core/libcore_generated.a is dirty
ninja explain: obj/third_party/WebKit/Source/core/css/libcss_5.a is dirty
ninja explain: obj/third_party/WebKit/Source/core/css/libcss_6.a is dirty
ninja explain: obj/third_party/WebKit/Source/core/css/libcss_7.a is dirty
ninja explain: obj/third_party/WebKit/Source/core/css/libcss_8.a is dirty
ninja explain: obj/third_party/WebKit/Source/core/css/libcss_9.a is dirty
...

Assigning to majidvp because this is likely https://chromium-review.googlesource.com/737090.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9bf5b69fa3541d4cd532c4681407bc0a53991bfd

commit 9bf5b69fa3541d4cd532c4681407bc0a53991bfd
Author: Majid Valipour <majidvp@chromium.org>
Date: Wed Oct 25 18:03:46 2017

Revert "Rename CSS scroll-boundary-behavior to overscroll-behavior"

This reverts commit 74e8a0f74fc589a58258655f59aa7f1efa666155.

Reason for revert: This caused an issue on Linux64 no-op build.
Bug:  778310 

Original change's description:
> Rename CSS scroll-boundary-behavior to overscroll-behavior
> 
> The name change was decided here [1]. 
> 
> This is the minimal patch to change the publicly exposed CSS property.
> It is intentionally small to make it easier to merge with M63. So, 
> internally Blink and content still use ScrollBoundaryBehavior name which will
> be updated in the follow up patch larger patch.
> 
> 
> [1] https://github.com/WICG/scroll-boundary-behavior/issues/24 
> 
> Bug:  776776 
> Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
> Change-Id: Iaa6ad62253ed7fe9ed7f0ee9865ffda852b17801
> Reviewed-on: https://chromium-review.googlesource.com/737090
> Reviewed-by: Dimitri Glazkov <dglazkov@chromium.org>
> Reviewed-by: Sandra Sun <sunyunjia@chromium.org>
> Commit-Queue: Majid Valipour <majidvp@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#511493}

TBR=majidvp@chromium.org,sunyunjia@chromium.org,dglazkov@chromium.org

Change-Id: I1d71b71c5d3c263fb2ff13c9d7a9184399df946f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  776776 
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Reviewed-on: https://chromium-review.googlesource.com/738294
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511515}
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/external/WPT_BASE_MANIFEST.json
[rename] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/external/wpt/cssom-view/scrollBoundaryBehavior-manual.html
[delete] https://crrev.com/2299d419e9087458847461509df9f6e8b7b23272/third_party/WebKit/LayoutTests/fast/css/getComputedStyle/getComputedStyle-overscrollBehavior-serialization.html
[add] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/fast/css/getComputedStyle/getComputedStyle-scrollBoundaryBehavior-serialization.html
[rename] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/fast/scroll-behavior/scroll-boundary-behavior.html
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/virtual/stable/webexposed/css-properties-as-js-properties-expected.txt
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/virtual/stable/webexposed/css-property-listing-expected.txt
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/webexposed/css-properties-as-js-properties-expected.txt
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/LayoutTests/webexposed/css-property-listing-expected.txt
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/BUILD.gn
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/CSSProperties.json5
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/CSSValueKeywords.json5
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/StylePropertySerializer.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp
[rename] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/css/properties/shorthands/CSSShorthandPropertyAPIScrollBoundaryBehavior.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/dom/Document.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/exported/WebFrameTest.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/frame/UseCounter.cpp
[delete] https://crrev.com/2299d419e9087458847461509df9f6e8b7b23272/third_party/WebKit/Source/core/input/OverscrollBehaviorTest.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/input/ScrollBoundaryBehaviorTest.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/input/ScrollManager.cpp
[modify] https://crrev.com/9bf5b69fa3541d4cd532c4681407bc0a53991bfd/third_party/WebKit/Source/core/paint/compositing/CompositedLayerMapping.cpp

 Issue 778511  has been merged into this issue.