The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6141310e2301e5a4e186e7fa661b5a365f0cb7fa

commit 6141310e2301e5a4e186e7fa661b5a365f0cb7fa
Author: Sandra Sun <sunyunjia@chromium.org>
Date: Mon Apr 09 22:24:43 2018

SnapFling support on cc should consider scaled case.

Currently, the current_offset and target_offset returned from layer_tree_host_impl are in the
coordinate of the page, but the parameters passed in ScrollBy() are in the coordinate of the
device. This inconsistency would cause the scroller to never reach the desired scroll offset if the
page is scaled.

This patch makes sure that all the scroll_offset returned from layer_tree_host_impl are in the
coordinate of the device, so that the snap_fling_controller can decide the correct value to scroll.

Bug:  827187 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I300a61f1fc2af9d7221d2d6f5f201fc461ada23f
Reviewed-on: https://chromium-review.googlesource.com/984902
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Sandra Sun <sunyunjia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549302}
[modify] https://crrev.com/6141310e2301e5a4e186e7fa661b5a365f0cb7fa/cc/input/input_handler.h
[modify] https://crrev.com/6141310e2301e5a4e186e7fa661b5a365f0cb7fa/cc/trees/layer_tree_host_impl.cc
[modify] https://crrev.com/6141310e2301e5a4e186e7fa661b5a365f0cb7fa/cc/trees/layer_tree_host_impl.h
[modify] https://crrev.com/6141310e2301e5a4e186e7fa661b5a365f0cb7fa/cc/trees/layer_tree_host_impl_unittest.cc
[modify] https://crrev.com/6141310e2301e5a4e186e7fa661b5a365f0cb7fa/ui/events/blink/snap_fling_controller.h