Add infrastructure for partial layouts

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index d4cada873fd79db991be809ab741937cbd2e69d6..9438070d270c70773ab277db525c65a61eaec337 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1744,6 +1744,9 @@ void Document::updateLayout()
     if (frameView && renderer() && (frameView->layoutPending() || renderer()->needsLayout()))
         frameView->layout();
 
+    if (frameView)
+        frameView->resetPartialLayoutState();
+
     setNeedsFocusedElementCheck();
 }
 
@@ -1790,6 +1793,26 @@ void Document::updateLayoutIgnorePendingStylesheets()
     m_ignorePendingStylesheets = oldIgnore;
 }
 
+void Document::tryPartialUpdateLayoutIgnorePendingStylesheets(RenderObject* stopLayoutAtRenderer)
+{
+    if (stopLayoutAtRenderer) {
+        // Look for parents that are css regions, flexbox, grid, or flow and prevent partial layout.
+        // FIXME: should this be a whitelist?
+        bool canDoPartialLayout = true;
+        RenderObject* renderer = stopLayoutAtRenderer;
+        do {
+            if (renderer->isFlexibleBoxIncludingDeprecated() || renderer->isRenderGrid() || renderer->isRenderRegion() || renderer->isRenderNamedFlowThread() || renderer->isRenderFlowThread()) {
+                canDoPartialLayout = false;
+                break;
+            }
+        } while ((renderer = renderer->parent()));
+        if (canDoPartialLayout)
+            view()->setStopLayoutAtRenderer(stopLayoutAtRenderer);
+    }
+
+    updateLayoutIgnorePendingStylesheets();
+}
+
 PassRefPtr<RenderStyle> Document::styleForElementIgnoringPendingStylesheets(Element* element)
 {
     ASSERT_ARG(element, element->document() == this);