Revert of Account for overlay scrollbars when computing scrollbar width/height.

Revert of Account for overlay scrollbars when computing scrollbar width/height. (patchset #4 id:60001 of https://codereview.chromium.org/2725763002/ )

Reason for revert:
A layout test gets red after this CL due to the mismatched test expectation.

The error log is:
https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.11%20%28retina%29/builds/13521

Original issue's description:
> Account for overlay scrollbars when computing scrollbar width/height.
> 
> This specifically addresses overlay scrollbars created via css with
> overflow:overlay.  In some places, those scrollbars are treated
> differently from overlay scrollbars created by the platform theme
> (e.g., on mac).
> 
> BUG=657718
> R=skobes@chromium.org
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
> 
> Review-Url: https://codereview.chromium.org/2725763002
> Cr-Commit-Position: refs/heads/master@{#454105}
> Committed: https://chromium.googlesource.com/chromium/src/+/5a729d1bc790d94120ec942a4566bb85f969cdb1

TBR=skobes@chromium.org,szager@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=657718

[tzik, 2017-03-16 02:08:05]

The CQ bit was checked by tzik@chromium.org

[tzik, 2017-03-16 02:08:05]

Created Revert of Account for overlay scrollbars when computing scrollbar
width/height.

[commit-bot: I haz the power, 2017-03-16 02:08:37]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-16 02:11:09]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-03-16 02:11:09]

Try jobs failed on following builders:
  ios-device on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/builds...)
  ios-simulator on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator/bui...)
  mac_chromium_compile_dbg_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)