[DevTools] Account for pointer-events:none when inspecting element from context menu.

I think most users expect that inspected element would be the one she interacts with.

BUG=371120

Review URL: https://codereview.chromium.org/282503002

git-svn-id: svn://svn.chromium.org/blink/trunk@173860 bbb929c8-8fbe-4397-9dbb-9b2b20218538