[UnifiedPDF] After resizing the window, PDF content is not centered a…

…nd hit testing is offset

https://bugs.webkit.org/show_bug.cgi?id=269549
rdar://123066513

Reviewed by Tim Horton.

The PDF content is centered in the window via a transform on the m_contentsLayer layer.
We need to update this transform both when the scale factor changes, but also when
layout is updated.

This is a small change to fix the issue. A larger refactoring of the "update" functions
is needed.

* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.h:
* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:
(WebKit::UnifiedPDFPlugin::updateLayerPositions):
(WebKit::UnifiedPDFPlugin::setPageScaleFactor):
(WebKit::UnifiedPDFPlugin::updateLayout):

Canonical link: https://commits.webkit.org/274859@main

Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.h

@@ -293,6 +293,7 @@ class UnifiedPDFPlugin final : public PDFPluginBase, public WebCore::GraphicsLay
     void ensureLayers();
     void updatePageBackgroundLayers();
     void updateLayerHierarchy();
+    void updateLayerPositions();
 
     void didChangeScrollOffset() override;
     void didChangeIsInWindow();

Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm

@@ -481,6 +481,16 @@ static String mutationObserverNotificationString()
     didChangeIsInWindow();
 }
 
+void UnifiedPDFPlugin::updateLayerPositions()
+{
+    TransformationMatrix transform;
+    transform.scale(m_scaleFactor);
+    auto padding = centeringOffset();
+    transform.translate(padding.width(), padding.height());
+
+    m_contentsLayer->setTransform(transform);
+    m_pageBackgroundsContainerLayer->setTransform(transform);
+}
 
 std::pair<bool, bool> UnifiedPDFPlugin::shouldShowDebugIndicators() const
 {
@@ -849,14 +859,7 @@ static String mutationObserverNotificationString()
     if (!m_inMagnificationGesture)
         m_rootLayer->noteDeviceOrPageScaleFactorChangedIncludingDescendants();
 
-    TransformationMatrix transform;
-    transform.scale(m_scaleFactor);
-    auto padding = centeringOffset();
-    transform.translate(padding.width(), padding.height());
-
-    m_contentsLayer->setTransform(transform);
-    m_pageBackgroundsContainerLayer->setTransform(transform);
-
+    updateLayerPositions();
     updatePageBackgroundLayers();
     updateSnapOffsets();
 
@@ -929,6 +932,7 @@ static String mutationObserverNotificationString()
     }
 
     updateLayerHierarchy();
+    updateLayerPositions();
     updateScrollingExtents();
 
     if (shouldAdjustScale == AdjustScaleAfterLayout::Yes && m_view) {