Fixed touch dragging of scrollbar thumbs on textarea.

The issue here was that touch adjustment was moving the touch point off
the scrollbar on the GestureShowPress, which activates scrollbar drag.
This patch changes the touch adjustment code to exit early if the touch
hits a scrollbar as the adjustment code considers only DOM nodes.
Additionally, to prevent additional hit testing, I changed the hit test
logic in the case of rect-based hit tests. The HitTestResult::append
method now copies the scrollbar result even if no node was hit. This
allows the rect-based hit test in adjustGesturePosition to return the
hit scrollbar.

BUG=272306

Review URL: https://codereview.chromium.org/62753003

git-svn-id: svn://svn.chromium.org/blink/trunk@162779 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove WEBKIT_HAS_TARGET_PING #define.

Chromium has removed its dependency on the #define.

BUG=302816
TEST=no behavior change.

Review URL: https://codereview.chromium.org/85003004

git-svn-id: svn://svn.chromium.org/blink/trunk@162780 bbb929c8-8fbe-4397-9dbb-9b2b20218538