Use PassRef for constructing StyleRules.
<https://webkit.org/b/123072>

Let functions that return newly-constructed StyleRuleFoo objects
vend PassRef<StyleRuleFoo> instead of PassRefPtr.

Since StyleRuleBase::copy() has to return something, we can't rely
on ASSERT_NOT_REACHED() + return nullptr anymore, so I've replaced
those with CRASH(). No call sites actually handled null anyway.

Reviewed by Sam Weinig.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@157698 268f45cc-cd09-0410-ab3c-d52691b4dbfc
[sh4] Fix build (broken since r157690).
https://bugs.webkit.org/show_bug.cgi?id=123081

Patch by Julien Brianceau <jbriance@cisco.com> on 2013-10-20
Reviewed by Andreas Kling.

* assembler/AssemblerBufferWithConstantPool.h:
* assembler/SH4Assembler.h:
(JSC::SH4Assembler::buffer):
(JSC::SH4Assembler::readCallTarget):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@157699 268f45cc-cd09-0410-ab3c-d52691b4dbfc