Remove redundant friending from class Image.
https://bugs.webkit.org/show_bug.cgi?id=130628

Reviewed by Simon Fraser.

Those friend classes are subclasses. No need to make them friend of their parent class.

No change in functionality.

* platform/graphics/Image.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@166111 268f45cc-cd09-0410-ab3c-d52691b4dbfc