[CSS Regions] Elements in a region should be assignable to a named flow

Source/core/dom/NodeRenderingContext.cpp

Index: Source/core/dom/NodeRenderingContext.cpp
diff --git a/Source/core/dom/NodeRenderingContext.cpp b/Source/core/dom/NodeRenderingContext.cpp
index 984dfb8de32a0fb39c3c389d53bd3afd829a6a97..8ea7f81fa8661c2292171d2cefdb14acd771c1cd 100644
--- a/Source/core/dom/NodeRenderingContext.cpp
+++ b/Source/core/dom/NodeRenderingContext.cpp
@@ -174,6 +174,7 @@ bool NodeRenderingContext::shouldCreateRenderer() const
 {
     if (!m_renderingParent)
         return false;
+
     RenderObject* parentRenderer = this->parentRenderer();
     if (!parentRenderer)
         return false;
@@ -184,37 +185,41 @@ bool NodeRenderingContext::shouldCreateRenderer() const
     return true;
 }
 
-void NodeRenderingContext::moveToFlowThreadIfNeeded()
+// Check the specific case of elements that are children of regions but are flowed into a flow thread themselves.
+bool NodeRenderingContext::elementInsideRegionNeedsRenderer()
 {
-    ASSERT(m_node->isElementNode());
-    ASSERT(m_style);
-    if (!RuntimeEnabledFeatures::cssRegionsEnabled())
-        return;
+    Element* element = toElement(m_node);
+    bool elementInsideRegionNeedsRenderer = false;
+    RenderObject* parentRenderer = this->parentRenderer();
+    if ((parentRenderer && !parentRenderer->canHaveChildren() && parentRenderer->isRenderRegion())
+        || (!parentRenderer && element->parentElement() && element->parentElement()->isInsideRegion())) {
 
-    if (m_style->flowThread().isEmpty())
-        return;
+        if (!m_style)
+            m_style = element->styleForRenderer();
 
-    // As per http://dev.w3.org/csswg/css3-regions/#flow-into, pseudo-elements such as ::first-line, ::first-letter, ::before or ::after
-    // cannot be directly collected into a named flow.
-    if (m_node->isPseudoElement())
-        return;
+        elementInsideRegionNeedsRenderer = element->shouldMoveToFlowThread(m_style.get());
 
-    // FIXME: Do not collect elements if they are in shadow tree.
-    if (m_node->isInShadowTree())
-        return;
+        // Children of this element will only be allowed to be flowed into other flow-threads if display is NOT none.
+        if (element->rendererIsNeeded(*this))
+            element->setIsInsideRegion(true);
+    }
 
-    if (m_node->isElementNode() && FullscreenController::isActiveFullScreenElement(toElement(m_node)))
+    return elementInsideRegionNeedsRenderer;
+}
+
+void NodeRenderingContext::moveToFlowThreadIfNeeded()
+{
+    if (!RuntimeEnabledFeatures::cssRegionsEnabled())
         return;
 
-    // Allow only svg root elements to be directly collected by a render flow thread.
-    if (m_node->isSVGElement()
-        && (!(m_node->hasTagName(SVGNames::svgTag) && m_node->parentNode() && !m_node->parentNode()->isSVGElement())))
+    Element* element = toElement(m_node);
+
+    if (!element->shouldMoveToFlowThread(m_style.get()))
         return;
 
-    m_flowThread = m_style->flowThread();
     ASSERT(m_node->document()->renderView());
     FlowThreadController* flowThreadController = m_node->document()->renderView()->flowThreadController();
-    m_parentFlowRenderer = flowThreadController->ensureRenderFlowThreadWithName(m_flowThread);
+    m_parentFlowRenderer = flowThreadController->ensureRenderFlowThreadWithName(m_style->flowThread());
     flowThreadController->registerNamedFlowContentNode(m_node, m_parentFlowRenderer);
 }
 
@@ -234,8 +239,11 @@ void NodeRenderingContext::createRendererForElementIfNeeded()
 
     Element* element = toElement(m_node);
 
-    if (!shouldCreateRenderer())
+    element->setIsInsideRegion(false);
+
+    if (!shouldCreateRenderer() && !elementInsideRegionNeedsRenderer())
         return;
+
     if (!m_style)
         m_style = element->styleForRenderer();
     ASSERT(m_style);