cache explosion issue due to css in style tags

[GoogleCodeExporter]

visit any site with large numbers of background-images in inline style tags.  
E.g. 

<h2 style="background-image:url(http://example.com/images/image1.png);">

Each one of these entries results in a small metadata cache entry.  
Additionally, due to the way we compute the cache key, if the same 
background-image is used in web pages with multiple paths, we will get distinct 
entries for each path.

This can be resolved by abstaining to write a metadata cache entry for such 
inline style attributes.  We should, of course, write the metadata cache entry 
for the image.

Of course we must plumb css_filter.cc/rewrite_context.cc to do the image 
substitution during the HTML rewrite.

Original issue reported on code.google.com by jmara...@google.com on 17 Oct 2012 at 3:04