This change fixes GC-leak caused by following mutual dependency:
- SVGDecodedImageData owns JS::Handle for Page.
- SVGDecodedImageData is owned by visited objects.
by making everything inherited from HTML::DecodedImageData and
ListOfAvailableImages to be GC-allocated.
Generally, if visited object has a handle, very likely we leak
everything visited from object in a handle.
Before this change, we used Gfx::Bitmap to represent both decoded
images that are not going to be mutated and bitmaps corresponding
to canvases that could be mutated.
This change introduces a wrapper for bitmaps that are not going to be
mutated, so the painter could do caching: texture caching in the case
of GPU painter and potentially scaled bitmap caching in the case of CPU
painter.
Before this change, whenever ImageStyleValue had a non-null
`m_image_request`, it was always leaked along with everything related
to the document to which this value belongs. The issue arises due to
the use of `JS::Handle` for the image request, as it introduces a
cyclic dependency where `ImageRequest` prevents the `CSSStyleSheet`,
that owns `ImageStyleValue`, from being deallocated:
- ImageRequest
- FetchController
- FetchParams
- Window
- HTMLDocument
- HTMLHtmlElement
- HTMLBodyElement
- Text
- HTMLHeadElement
- Text
- HTMLMetaElement
- Text
- HTMLTitleElement
- Text
- HTMLStyleElement
- CSSStyleSheet
This change solves this by visiting `m_image_request` from
`visit_edges` instead of introducing new heap root by using
`JS::Handle`.
This allows to partially solve the problem of cyclic dependency between
HTMLImageElement and SharedImageRequest that prevents all image
elements from being deallocated.
As it turns out, making everyone piggyback on HTML::ImageRequest had
some major flaws, as HTMLImageElement may decide to abort an ongoing
fetch or wipe out image data, even when someone else is using the same
image request.
To avoid this issue, this patch introduces SharedImageRequest, and then
implements ImageRequest on top of that.
Other clients of the ImageRequest API are moved to SharedImageRequest
as well, and ImageRequest is now only used by HTMLImageElement.
This fixes an issue with image data disappearing and leading to asserts
and/or visually absent images.
This is all ad-hoc since no spec currently exists for this behavior.
Basically, ImageStyleValue now uses ImageRequest for fetching and
decoding of images.
This already leads to visible improvements on many websites.
