DevTools: resolve layer owner nodes while importing layer tree from trace

Also, retain layer object instances when updating the same layer,
as we used to do with AgentLayers.

BUG=361045

Review URL: https://codereview.chromium.org/291563005

git-svn-id: svn://svn.chromium.org/blink/trunk@174293 bbb929c8-8fbe-4397-9dbb-9b2b20218538