https://bugs.webkit.org/show_bug.cgi?id=85004

Reviewed by Andreas Kling.

CSS parsing is 1-2% of WebKit CPU usage on average pages, more on sites with large stylesheets.
We currently reparse all stylesheets from source text when they are encountered again. In many
browsing scenarios we can eliminate lot of this by caching the parsed stylesheets. For example 
it is very common for subpages of a site to share the stylesheets.
        
This patch enables memory caching for stylesheet loaded using the <link> element. Only stylesheets
that have no import rules are cacheable for now.
        
Cached stylesheets are copied on restore so there is no sharing (and no memory wins) yet.
In the future we will also be able to share the actual data structures between pages for 
significant memory savings.
        
After browsing around for a while <5% of the memory cache data was in parsed stylesheets so this
does not bloat the cache significantly.

* css/CSSStyleSheet.cpp:
(WebCore):
(WebCore::StyleSheetInternal::estimatedSizeInBytes):
        
    Estimate stylesheet size so we can handle decoded data pruning correctly.

* css/CSSStyleSheet.h:
(StyleSheetInternal):
* css/StylePropertySet.cpp:
(WebCore::StylePropertySet::averageSizeInBytes):
(WebCore):
* css/StylePropertySet.h:
(StylePropertySet):
* css/StyleRule.cpp:
(WebCore::StyleRule::averageSizeInBytes):
(WebCore):
* css/StyleRule.h:
(StyleRule):
* html/HTMLLinkElement.cpp:
(WebCore::HTMLLinkElement::setCSSStyleSheet):
        
    Save and restore parsed stylesheet. The current CSS parse context must be identical to the cached 
    stylesheets. This ensures that the parsing results would be identical.

* loader/cache/CachedCSSStyleSheet.cpp:
(WebCore):
(WebCore::CachedCSSStyleSheet::destroyDecodedData):
(WebCore::CachedCSSStyleSheet::restoreParsedStyleSheet):
(WebCore::CachedCSSStyleSheet::saveParsedStyleSheet):
* loader/cache/CachedCSSStyleSheet.h:
        
    The parsed stylesheet cache is considered decoded data, similar to the image bitmaps. It uses the
    same mechanism for pruning.

(WebCore):
(CachedCSSStyleSheet):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@115379 268f45cc-cd09-0410-ab3c-d52691b4dbfc