Bug 269244 – [UnifiedPDF] Crash when scrolling after a swipe back from an external link follow

• Component: PDF
• Status: RESOLVED FIXED

[Abrar Rahman Protyasha]

If we click to follow an external link, then swiping back and scrolling on the original PDF document causes a crash. Here is a snippet of the crash log.

```
Thread 0 Crashed::  Dispatch queue: com.apple.main-thread
0   JavaScriptCore                	       0x12c6a2f18 WTFCrash + 24 (Assertions.cpp:351)
1   WebCore                       	       0x14d6ff624 WTFCrashWithInfo(int, char const*, char const*, int) + 36 (Assertions.h:780)
2   WebCore                       	       0x14f321f80 WebCore::LayerRepresentation::operator CALayer*() const + 128 (ScrollingStateNode.h:106)
3   WebCore                       	       0x14f5851e0 WebCore::ScrollingTreePluginScrollingNodeMac::repositionScrollingLayers() + 48 (ScrollingTreePluginScrollingNodeMac.mm:103)
4   WebCore                       	       0x1528f59f8 WebCore::ScrollingTreeScrollingNode::applyLayerPositions() + 68 (ScrollingTreeScrollingNode.cpp:392)
5   WebCore                       	       0x1528ddd88 WebCore::ScrollingTree::applyLayerPositionsRecursive(WebCore::ScrollingTreeNode&) + 76 (ScrollingTree.cpp:498)
6   WebCore                       	       0x1528ddde4 WebCore::ScrollingTree::applyLayerPositionsRecursive(WebCore::ScrollingTreeNode&) + 168 (ScrollingTree.cpp:501)
7   WebCore                       	       0x1528ddde4 WebCore::ScrollingTree::applyLayerPositionsRecursive(WebCore::ScrollingTreeNode&) + 168 (ScrollingTree.cpp:501)
8   WebCore                       	       0x1528ddd2c WebCore::ScrollingTree::applyLayerPositionsInternal() + 176 (ScrollingTree.cpp:493)
9   WebCore                       	       0x1528ddc68 WebCore::ScrollingTree::applyLayerPositions() + 96 (ScrollingTree.cpp:484)
10  WebCore                       	       0x1528ddbf8 WebCore::ScrollingTree::applyLayerPositionsAfterCommit() + 92 (ScrollingTree.cpp:477)
11  WebKit                        	       0x11527c49c WebKit::RemoteScrollingCoordinatorProxy::applyScrollingTreeLayerPositionsAfterCommit() + 56 (RemoteScrollingCoordinatorProxy.cpp:162)
12  WebKit                        	       0x1149c6aa8 WebKit::RemoteScrollingCoordinatorProxyMac::applyScrollingTreeLayerPositionsAfterCommit() + 32 (RemoteScrollingCoordinatorProxyMac.mm:291)
13  WebKit                        	       0x114992ec4 WebKit::RemoteLayerTreeDrawingAreaProxy::commitLayerTreeTransaction(IPC::Connection&, WebKit::RemoteLayerTreeTransaction const&, WebKit::RemoteScrollingCoordinatorTransaction const&) + 2028 (RemoteLayerTreeDrawingAreaProxy.mm:305)
```

[Radar WebKit Bug Importer]

<rdar://problem/122835175>

[Simon Fraser (smfr)]

Pull request: https://github.com/WebKit/WebKit/pull/24854

[EWS]

Committed 275123@main (a55bd5c3df1c): <https://commits.webkit.org/275123@main>

Reviewed commits have been landed. Closing PR #24854 and removing active labels.