Improve scroll performance of WebInspector.TreeOutlineDataGridSynchronizer.

https://bugs.webkit.org/show_bug.cgi?id=126660

Reviewed by Joseph Pecoraro.

* UserInterface/TreeOutlineDataGridSynchronizer.js:
(WebInspector.TreeOutlineDataGridSynchronizer.prototype._treeOutlineScrolled):
(WebInspector.TreeOutlineDataGridSynchronizer.prototype._dataGridScrolled):
Ignore scroll events triggered by our internal use of setting scrollTop.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162406 268f45cc-cd09-0410-ab3c-d52691b4dbfc