Reduce refcount of SharedMemory when sending them over IPC.

[jyavenard]

6a4bb0e

Reduce refcount of SharedMemory when sending them over IPC.
https://bugs.webkit.org/show_bug.cgi?id=240855
rdar://problem/93806688

Reviewed by Jer Noble.

In the future, we want to be able to donate memory with exclusive access to another process, this require the VM to have a refcount of 1.
No change in obeservable behaviour. Covered by existing tests.

* Source/WebKit/Shared/WebCoreArgumentCoders.cpp:
(IPC::encodeSharedBuffer):
* Source/WebKit/UIProcess/Cocoa/WebPasteboardProxyCocoa.mm:
(WebKit::WebPasteboardProxy::getPasteboardBufferForType):
(WebKit::WebPasteboardProxy::readBufferFromPasteboard):
* Source/WebKit/WebProcess/GPU/media/RemoteMediaResourceProxy.cpp:
(WebKit::RemoteMediaResourceProxy::dataReceived):
* Source/WebKit/WebProcess/GPU/media/SourceBufferPrivateRemote.cpp:
(WebKit::SourceBufferPrivateRemote::append):
* Source/WebKit/WebProcess/Plugins/PDF/PDFPlugin.mm:
(WebKit::PDFPlugin::writeItemsToPasteboard):
* Source/WebKit/WebProcess/WebCoreSupport/mac/WebDragClientMac.mm:
(WebKit::WebDragClient::declareAndWriteDragImage):
* Source/WebKit/WebProcess/WebPage/ios/WebPageIOS.mm:
(WebKit::WebPage::performActionOnElement):
(WebKit::WebPage::didFinishLoadForQuickLookDocumentInMainFrame):
* Source/WebKit/WebProcess/WebPage/mac/WebPageMac.mm:
(WebKit::WebPage::getDataSelectionForPasteboard):

Canonical link: https://commits.webkit.org/250943@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@294784 268f45cc-cd09-0410-ab3c-d52691b4dbfc

[jernoble]

Nit: This could just be SharedMemory::copyBuffer(data)->createHandle(handle, SharedMemory::Protection::ReadOnly); without the braces.

[jyavenard]

actually, this is wrong; copyBuffer can return nullptr; we should null check here.

[jernoble]

r=me, with a nit inline.

[webkit-early-warning-system]

Committed r294784 (250943@main): https://commits.webkit.org/250943@main

Reviewed commits have been landed. Closing PR #971 and removing active labels.