[CSSRegions] Make RenderNamedFlowFragment::computeStyleInRegion const
https://bugs.webkit.org/show_bug.cgi?id=137604

Reviewed by Andrei Bucur.

The method computeStyleInRegion should be const as it does not modify
the state of the RenderNamedFlowFragment instance. Make pointers to
the region used for styling const along the way. No new tests as no
change in functionality.

* css/ElementRuleCollector.h:
(WebCore::ElementRuleCollector::ElementRuleCollector):
(WebCore::ElementRuleCollector::setRegionForStyling):
* css/StyleResolver.cpp:
(WebCore::StyleResolver::State::initForStyleResolve):
(WebCore::StyleResolver::styleForElement):
* css/StyleResolver.h:
* rendering/RenderNamedFlowFragment.cpp:
(WebCore::RenderNamedFlowFragment::computeStyleInRegion):
* rendering/RenderNamedFlowFragment.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@174648 268f45cc-cd09-0410-ab3c-d52691b4dbfc