ImageBufferBackend::clearContents() is redundant function

[kkinnunen-apple]

433f175

ImageBufferBackend::clearContents() is redundant function
https://bugs.webkit.org/show_bug.cgi?id=253065
rdar://problem/106020763

Reviewed by Antti Koivisto.

Remove ImageBuffer{,Backend}::clearContents(), it is only implemented
for CG display list -backed ImageBuffers.

Use ImageBuffer::releaseGraphicsContext() to remove all commands to
CG display list -backed ImageBuffer. This should stay consistent with the
abstraction that the caller expects: For the purposes of the call, e.g.
ensuring that the list does not grow indefinitively, it is expected that
the relevant draw commands are part of the context.

* Source/WebCore/platform/graphics/ImageBuffer.cpp:
(WebCore::ImageBuffer::clearContents): Deleted.
* Source/WebCore/platform/graphics/ImageBuffer.h:
* Source/WebCore/platform/graphics/ImageBufferBackend.h:
(WebCore::ImageBufferBackend::clearContents): Deleted.
* Source/WebKit/Shared/RemoteLayerTree/CGDisplayListImageBufferBackend.h:
* Source/WebKit/Shared/RemoteLayerTree/CGDisplayListImageBufferBackend.mm:
(WebKit::CGDisplayListImageBufferBackend::releaseGraphicsContext):
(WebKit::CGDisplayListImageBufferBackend::clearContents): Deleted.
* Source/WebKit/Shared/RemoteLayerTree/RemoteLayerBackingStore.mm:
(WebKit::RemoteLayerBackingStore::swapToValidFrontBuffer):

Canonical link: https://commits.webkit.org/261057@main

ab3d05a

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🛠 gtk
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	❌ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash ab3d05a)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🛠 gtk
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	❌ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 261057@main (433f175): https://commits.webkit.org/261057@main

Reviewed commits have been landed. Closing PR #10787 and removing active labels.