Since more DOM nodes are going to want to load images (<object>, ...)
this patch splits out the image loading logic into an ImageLoader class
and then HTMLImageElement simply has an ImageLoader.
LayoutImage is then given a const ImageLoader& at construction and can
then provide layout and rendering for many kinds of DOM nodes.
This patch adds ImageResource as a subclass of Resource. This new class
also keeps a Gfx::ImageDecoder so that we can share decoded bitmaps
between all clients of an image resource inside LibWeb.
With this, we now share both encoded and decoded data for images. :^)
I had to change how the purgeable-volatile flag is updated to keep the
volatile-images-outside-the-visible-viewport optimization working.
HTMLImageElement now inherits from ImageResourceClient (a subclass of
ResourceClient with additional image-specific stuff) and informs its
ImageResource about whether it's inside the viewport or outside.
This is pretty awesome! :^)
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.
