Trackpad scrolling while columns pinned unexpectedly scrolls parent container

[JoshuaBrinkley]

Environment:

• UI-Grid Version 4.0.2 (stable)
• Starting from tutorial 203-pinning; modified in plunker for alternate pinning configurations (i.e. left pin only, right pin only) as well as testing using the ui-grid-unstable.js version.
• Trackpad with two-finger vertical & horizontal scrolling
• Tested on macOS 10.12.3
• Tested using Chrome 58.0.3029.19 beta (64-bit)
• Tested using Safari 10.0.3 (12602.4.8)
• 1st Note: Not experienced when columns are not pinned.
• 2nd Note: Not normally experienced while using mouse wheel traditionally with mutually exclusive vertical/horizontal scrolling i.e. horizontal scroll requires shift or other modifier key.

Expected Behaviors:

• While mouse pointer is over any part of the grid, scrolling vertically only affects the grid's vertically scrollable area(s) until reaching the top most scrollable row while scrolling up and bottom most scrollable row while scrolling down. When exceeding these boundaries, the parent container is expected to scroll vertically in the intended direction.
• While mouse pointer is over any part of the grid, scrolling horizontally only affects the horizontally scrollable grid area(s) until reaching the left most scrollable column while scrolling left and right most scrollable column while scrolling right. When exceeding these boundaries, the parent container is expected to scroll horizontally in the intended direction.

Current Behavior:

• While mouse pointer is over left pinned column, scrolling over the column diagonally with a trackpad motion down and right while mouse point remains in the left pinned column, the parent container scrolls up.
• While mouse pointer is over left pinned column, scrolling over the column diagonally with a trackpad motion up and right while mouse point remains in the left pinned column, the parent container scrolls down.
• While mouse pointer is over unpinned scrollable columns and left most scrollable column is fully in view, scrolling over the column diagonally with a trackpad motion down and right while mouse point remains in the unpinned columns, the parent container scrolls up.
• While mouse pointer is over unpinned scrollable columns and left most scrollable column is fully in view, scrolling over the column diagonally with a trackpad motion up and right while mouse point remains in the unpinned columns, the parent container scrolls down.
• While mouse pointer is over unpinned scrollable columns and right most scrollable column is fully in view, scrolling over the column diagonally with a trackpad motion down and left while mouse point remains in the unpinned columns, the parent container scrolls up.
• While mouse pointer is over unpinned scrollable columns and right most scrollable column is fully in view, scrolling over the column diagonally with a trackpad motion up and left while mouse point remains in the unpinned columns, the parent container scrolls down.

Additional Notes:

• Possible duplicate of RTL: scrolling janky/not working on OSX trackpad #1689 but not entirely sure
• Experienced the symptoms of Horizontal scroll on pinned column causes grid to scroll to rightmost border #4037 while testing.
• Experienced the symptoms mentioned in "Blank content" when scroll fast in ui-grid #3643 while scrolling from the right most column to the left most column very quickly (usually after a flick gesture)