[Site Isolation] Resizing the window causes rendering issues inside c…

…ross-origin iframe.

https://bugs.webkit.org/show_bug.cgi?id=272419
<rdar://126160881>

Reviewed by Alex Christensen.

When Page::layoutIfNeeded tries to layout all documents (and flush their compositing
layers), it should do so for all root frames, not just the main frame.

* Source/WebCore/page/Page.cpp:
(WebCore::Page::layoutIfNeeded):

Canonical link: https://commits.webkit.org/277339@main

LayoutTests/http/tests/site-isolation/scrolling/basic-scrolling-tree-expected.txt

@@ -21,15 +21,15 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
     (frame hosting node
       (has hosting context identifier )
       (frame scrolling node
-        (scrollable area size width=800 height=600)
-        (total content size width=800 height=600)
+        (scrollable area size width=300 height=300)
+        (total content size width=300 height=300)
         (last committed scroll position (0,0))
         (scrollable area parameters
           (horizontal scroll elasticity 0)
           (vertical scroll elasticity 0)
           (horizontal scrollbar mode 0)
           (vertical scrollbar mode 0))
-        (layout viewport (0,0) width=800 height=600)
+        (layout viewport (0,0) width=300 height=300)
         (min layoutViewport origin (0,0))
         (max layoutViewport origin (0,0))
         (behavior for fixed 1)))))

Source/WebCore/page/Page.cpp

@@ -1760,9 +1760,14 @@ void Page::removeActivityStateChangeObserver(ActivityStateChangeObserver& observ
 
 void Page::layoutIfNeeded(OptionSet<LayoutOptions> layoutOptions)
 {
-    auto* localMainFrame = dynamicDowncast<LocalFrame>(m_mainFrame.get());
-    if (RefPtr view = localMainFrame ? localMainFrame->view() : nullptr)
+    for (auto& rootFrame : m_rootFrames) {
+        ASSERT(rootFrame->isRootFrame());
+        RefPtr view = rootFrame->view();
+        if (!view)
+            continue;
+
         view->updateLayoutAndStyleIfNeededRecursive(layoutOptions);
+    }
 }
 
 void Page::scheduleRenderingUpdate(OptionSet<RenderingUpdateStep> requestedSteps)