Use display width for touchpad overscroll activation threshold

The activation threshold for touchpad overscroll is updated to be based
on display width/height rather than window width/height.  Touchscreen
overscroll still uses window width/height.

BUG=668296
TEST=none

Change-Id: Ie98151825784c36633f27ea2f4ce4fac9906e43e
Reviewed-on: https://chromium-review.googlesource.com/526412
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Mikhail Fomitchev <mfomitchev@chromium.org>
Commit-Queue: Mohsen Izadi <mohsen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#483739}

• content/browser/renderer_host/input/touch_selection_controller_client_aura_browsertest.cc[diff]
• content/browser/renderer_host/overscroll_configuration.cc[diff]
• content/browser/renderer_host/overscroll_controller.cc[diff]
• content/browser/renderer_host/overscroll_controller.h[diff]
• content/browser/renderer_host/overscroll_controller_delegate.h[diff]
• content/browser/renderer_host/render_widget_host_view_aura_unittest.cc[diff]
• content/browser/web_contents/aura/gesture_nav_simple.cc[diff]
• content/browser/web_contents/aura/gesture_nav_simple.h[diff]
• content/browser/web_contents/aura/overscroll_window_animation.cc[diff]
• content/browser/web_contents/aura/overscroll_window_animation.h[diff]
• content/browser/web_contents/aura/overscroll_window_delegate.cc[diff]
• content/browser/web_contents/aura/overscroll_window_delegate.h[diff]
• content/browser/web_contents/aura/overscroll_window_delegate_unittest.cc[diff]
• content/browser/web_contents/web_contents_view_aura.cc[diff]
• content/browser/web_contents/web_contents_view_aura.h[diff]
• content/public/browser/overscroll_configuration.h[diff]