Clarify/fix {Shadow,BorderImage}ParseContext's memory management

Clarify/fix {Shadow,BorderImage}ParseContext's memory management

Prefast emitted warnings that drew my attention to
{Shadow,BorderImage}ParseContext::failed().  It turned out that these
methods were actually correct, but rather confusing. "failed" really
meant "abort and clean up" rather than "did you fail?", which was
unclear. However, once I figured that out, the "and clean up" part was
still a bit confusing, because all failed() did was to set a flag that
would later cause the ParseContext's members to be deleted in the
destructor. To clear this up, I've gotten rid of the failed() method
altogether. It always returned false, so I've replaced all calls to
it with the value false.

I also noticed that the lifetime management of the ParseContexts'
members was in all cases confusing, and in some cases wrong. The
m_border{Top,Right,Bottom,Left} members of BorderImageParseContext
were leaked whenever a border-image property was successfully parsed.
I fixed that by holding these members in OwnPtrs. The
CSSPrimitiveValue members of {Shadow,BorderImage}ParseContext, which
inherit from Shared, were being explicitly deleted, which is not a
safe way to manage the lifetime of objects that inherit from Shared.
To fix this, I put those members inside RefPtrs. These two changes
allowed me to remove the destructors entirely.

Reviewed by Darin.

All regression tests pass.

* css/cssparser.cpp:
(WebCore::ShadowParseContext::commitValue): Use .release() to avoid
ref-count churn.
(WebCore::ShadowParseContext::commitLength): Use a RefPtr for the new value to
avoid a leak.
(WebCore::CSSParser::parseShadow): Use 'false' instead of
'context.failed()', and use .release() to avoid ref-count churn.
(WebCore::BorderImageParseContext::commitWidth): Updated to use
OwnPtr.
(WebCore::CSSParser::parseBorderImage): Use 'false' instead of
'context.failed'.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@23925 268f45cc-cd09-0410-ab3c-d52691b4dbfc