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This patch does the following:
1. Moves the data structure of SnapPoints from blink to cc and shares it back with blink.
2. Use the coordinate of ScrollPosition and the type of FloatPoint to do calculations in
   SnapCoordinator instead of ScrollOffset, as gfx::ScrollOffset uses ScrollPosition.
3. Update the logic in SnapCoordinator to work with vertical-rl writing-mode.
4. Use LocalToAncestorQuad() for the snap_area to ensure transforms are properly dealt with.


Bug: 795404
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I538327e169ebee4d3e03ec2ddd0d5b282e36f5de
Reviewed-on: https://chromium-review.googlesource.com/825994Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Commit-Queue: Sandra Sun <sunyunjia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525271}