DevTools: InspectorHistory actions become refcounted.

This patch makes InspectorHistory::Action class to be refcounted. This
helps to get results of completed operations in InspectorHistory without
possibility of use-after-free (this patch fixes two of this cases).

BUG=

Review URL: https://codereview.chromium.org/208893007

git-svn-id: svn://svn.chromium.org/blink/trunk@170054 bbb929c8-8fbe-4397-9dbb-9b2b20218538