Remove hard coded leading slash in head_tag.cs for DevSite image_path meta tag. am: c9ef9fea7f am: ea99b7d8bd am: 065e5e3fac am: a7776e5bb9
am: d0f14a9966

Change-Id: Ia1fd4f8d775339ba7a6eb007a1730dfd0fcbcbb0