This patch introduces a caching mechanism in ResourceLoader. It's keyed
on a LoadRequest object which is what you provide to load_resource()
when you want to load a resource.
We currently never prune the cache, so resources will stay in there
forever. This is obviously not gonna stay that way, but we're just
getting started here. :^)
This should drastically reduce the number of requests when loading
some sites (like Twitter) that reuse the same images over and over.
A Resource represents a resource that we're loading, have loaded or
will soon load. Basically, it's a downloadable resource that can be
shared by multiple clients.
A typical usecase is multiple <img> elements with the same src.
In a future patch, we will try to make sure that those <img> elements
get the same Resource if possible. This will reduce network usage,
memory usage, and CPU usage. :^)
For now, this first patch simply introduces the mechanism.
You get a Resource by calling ResourceLoader::load_resource().
To get notified about changes to a Resource's load status, you inherit
from ResourceClient and implement the callbacks you're interested in.
This patch turns HTMLImageElement into a ResourceClient.
