Make some things that return never-null pointers return references instead.
<http://webkit.org/b/119660>

Reviewed by Antti Koivisto.

Source/WebCore:

These functions never return null anyway, so remove any ambiguity by letting
them return references instead of pointers.

- Node::ensureRareData()
- Element::ensureUniqueElementData()
- Element::ensureShadow()
- Element::ensureUserAgentShadowRoot()
- StyledElement::ensureMutableInlineStyle()
- NodeRareData::ensureNodeLists()
- NodeRareData::ensureMutationObserverData()
- EventTarget::ensureEventTargetData()
- Document::ensureStyleResolver()
- Document::selectorQueryCache()
- Document::mediaQueryMatcher()
- FlowThreadController::ensureRenderFlowThreadWithName()
- HTMLTrackElement::ensureTrack()
- SVGElement::ensureSVGRareData()
- AnimationControllerPrivate::ensureCompositeAnimation()

Source/WebKit/qt:

* Api/qwebelement.cpp:
(QWebElement::styleProperty):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153926 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Make Page::settings() return a reference.
<http://webkit.org/b/119662>

Reviewed by Anders Carlsson.

...and remove some pointless null checks that were exposed by doing this.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153927 268f45cc-cd09-0410-ab3c-d52691b4dbfc