The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b3f07f124135e81072377bd9da56d19a4976c3df

commit b3f07f124135e81072377bd9da56d19a4976c3df
Author: Sandra Sun <sunyunjia@chromium.org>
Date: Wed Mar 21 18:46:21 2018

Implement scroll-snap-type: proximity

As specified in the spec, when the snap-container has scroll-snap-type:
proximity, we should only consider snap positions that are close to the
current scroll offset.
https://drafts.csswg.org/css-scroll-snap-1/#snap-strictness

Bug:  823820 
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I6312f98df421e303eb538f422ede39cea8dd5d38
Reviewed-on: https://chromium-review.googlesource.com/971466
Commit-Queue: Sandra Sun <sunyunjia@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544783}
[modify] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/cc/input/scroll_snap_data.cc
[modify] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/cc/input/scroll_snap_data.h
[modify] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/cc/input/scroll_snap_data_unittest.cc
[add] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/third_party/WebKit/LayoutTests/external/wpt/css/css-scroll-snap/scroll-snap-type-proximity.html
[modify] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.cpp
[modify] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h
[modify] https://crrev.com/b3f07f124135e81072377bd9da56d19a4976c3df/third_party/WebKit/Source/core/page/scrolling/SnapCoordinatorTest.cpp