Purge PassRefPtr from Page.

Purge PassRefPtr from Page.
<https://webkit.org/b/140089>

Reviewed by Anders Carlsson.

Source/WebCore:

Use Ref or RefPtr instead of PassRefPtr as appropriate in WebCore::Page.

* page/Page.cpp:
(WebCore::Page::rangeOfString):
(WebCore::Page::setSessionStorage):
* page/Page.h:
* page/mac/PageMac.cpp:
(WebCore::Page::addSchedulePair):
(WebCore::Page::removeSchedulePair):

Source/WTF:

Make SchedulePair::create() return Ref since it never fails.

* wtf/SchedulePair.h:
(WTF::SchedulePair::create):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@177929 268f45cc-cd09-0410-ab3c-d52691b4dbfc