Just a little additional information:
I have installed plank on ubuntu 14.10 (unity), if I start Chrome from plank a new (low-res) icon is created in both plank and unity launcher.
If I launch chrome from Unity launcher the second Icon doesn't appear in unity launcher nor in plank.
So to resume: only when launched from plank an additional icon is created.
Just a little additional information:
I have installed plank on ubuntu 14.10 (unity), if I start Chrome from plank a new (low-res) icon is created in both plank and unity launcher.
If I launch chrome from Unity launcher the second Icon doesn't appear in unity launcher nor in plank.
So to resume: only when launched from plank an additional icon is created.