Revert of Remove enable/disable wheel gestures setting. (patchset #3 id:40001 of https://codereview.chromium.org/2047093002/ )

Reason for revert:
Caused RenderWidgetHostViewMacTest.IgnoreEmptyUnhandledWheelEventWithWheelGestures failure on build:

https://build.chromium.org/p/chromium.mac/builders/Mac10.9%20Tests%20(dbg)/builds/25325

See
https://findit-for-me.appspot.com/build-failure?url=https://build.chromium.org/p/chromium.mac/builders/Mac10.9%20Tests%20(dbg)/builds/25325

Test output:
"""
[ RUN      ] RenderWidgetHostViewMacTest.IgnoreEmptyUnhandledWheelEventWithWheelGestures
../../content/browser/renderer_host/render_widget_host_view_mac_unittest.mm:966: Failure
Value of: view_delegate.get().unhandledWheelEventReceived
  Actual: ''
Expected: __objc_yes
Which is: '?' (1)
[3372:1287:0608/164121:1128775946716:FATAL:surface_manager.cc(43)] Check failed: namespace_client_map_.size() == 0u (1 vs. 0)
"""

Original issue's description:
> Remove enable/disable wheel gestures setting.
>
> Since wheel gesture based scrolling has shipped and the code has been
> removed from blink we can remove the runtime setting.
>
> BUG=598798
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/3f5cea527647ebc8c505b1932d680854e162d82f
> Cr-Commit-Position: refs/heads/master@{#398716}

TBR=aelias@chromium.org,rbyers@chromium.org,creis@chromium.org,dtapuska@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=598798

Review-Url: https://codereview.chromium.org/2050033002
Cr-Commit-Position: refs/heads/master@{#398746}
38 files changed