Create resizer for allocation perspective split view

Now there is a resizer between Allocations data grid and live objects summary view. The resizer has the same look as the one in the summary perspective.

BUG=277984
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/221863002

git-svn-id: svn://svn.chromium.org/blink/trunk@170659 bbb929c8-8fbe-4397-9dbb-9b2b20218538