[Mac] Remove call to ClipboardMac::create from Editor::newGeneralClipboard
https://bugs.webkit.org/show_bug.cgi?id=116162

Reviewed by Andreas Kling.

* dom/Clipboard.h: Add createForCopyAndPaste function.

* editing/mac/EditorMac.mm:
(WebCore::Editor::newGeneralClipboard): Call createForCopyAndPaste.

* platform/mac/ClipboardMac.mm:
(WebCore::Clipboard::createForCopyAndPaste): Added. Moved code here from
Editor::newGeneralClipboard.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150125 268f45cc-cd09-0410-ab3c-d52691b4dbfc