Implement lazy block layout prototype behind a runtime flag.

Source/core/page/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 50 matching lines @@
 #include "core/platform/graphics/FontCache.h"
 #include "core/platform/graphics/GraphicsContext.h"
 #include "core/platform/text/TextStream.h"
 #include "core/rendering/RenderArena.h"
 #include "core/rendering/RenderEmbeddedObject.h"
 #include "core/rendering/RenderFullScreen.h"
 #include "core/rendering/RenderIFrame.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderLayerBacking.h"
 #include "core/rendering/RenderLayerCompositor.h"
+#include "core/rendering/RenderLazyBlock.h"
 #include "core/rendering/RenderPart.h"
 #include "core/rendering/RenderScrollbar.h"
 #include "core/rendering/RenderScrollbarPart.h"
 #include "core/rendering/RenderTheme.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/TextAutosizer.h"
 #include "core/rendering/style/RenderStyle.h"
 
 #include <wtf/CurrentTime.h>
 #include <wtf/TemporaryChange.h>
@@ skipping 1031 matching lines @@
     endDeferredRepaints();
 
     updateCompositingLayersAfterLayout();
 
     m_layoutCount++;
 
     if (AXObjectCache* cache = root->document()->existingAXObjectCache())
         cache->postNotification(root, AXObjectCache::AXLayoutComplete, true);
     updateAnnotatedRegions();
 
+    layoutLazyBlocks();
+
     ASSERT(!root->needsLayout());
 
     updateCanBlitOnScrollRecursively();
 
     if (document->hasListenerType(Document::OVERFLOWCHANGED_LISTENER))
         updateOverflowStatus(layoutWidth() < contentsWidth(),
                              layoutHeight() < contentsHeight());
 
     if (!m_postLayoutTasksTimer.isActive()) {
         if (!m_inSynchronousPostLayout) {
@@ skipping 29 matching lines @@
     if (m_nestedLayoutCount)
         return;
 
     Page* page = frame() ? frame()->page() : 0;
     if (!page)
         return;
 
     page->chrome()->client()->layoutUpdated(frame());
 }
 
+void FrameView::layoutLazyBlocks()
+{
+    // FIXME: This infinite recursion protection would seem to break plugins
+    // doing things that require lazy blocks to layout.
+    if (m_nestedLayoutCount != 1)
+        return;
+
+    if (!renderView()->firstLazyBlock())

[eseidel, 2013/04/27 09:09:34]

Is this expensive?

+        return;
+
+    // First mark all lazy blocks as needing layout and perform another layout.
+    for (RenderLazyBlock* block = renderView()->firstLazyBlock(); block; block = block->next())
+        block->markForNestedLayout();
+
+    layout();
+
+    // FIXME: This is pretty awful if you start nesting lazy blocks, we should
+    // signal to the nested blocks to avoid doing work until the second pass.
+
+    // Next walk all lazy blocks and find nested ones, these need another layout
+    // since the first one would not have placed them correctly inside the viewport.
+    for (RenderLazyBlock* block = renderView()->firstLazyBlock(); block; block = block->next()) {
+        if (!block->isNested())
+            continue;
+        block->setNeedsLayout(true);
+        layout();
+    }
+}
+
 RenderBox* FrameView::embeddedContentBox() const
 {
 #if ENABLE(SVG)
     RenderView* renderView = this->renderView();
     if (!renderView)
         return 0;
 
     RenderObject* firstChild = renderView->firstChild();
     if (!firstChild || !firstChild->isBox())
         return 0;
@@ skipping 456 matching lines @@
 
 
 void FrameView::scrollPositionChanged()
 {
     frame()->eventHandler()->sendScrollEvent();
     frame()->eventHandler()->dispatchFakeMouseMoveEventSoon();
 
     if (RenderView* renderView = this->renderView()) {
         if (renderView->usesCompositing())
             renderView->compositor()->frameViewDidScroll();
+
+        renderView->markLazyBlocksForLayout();
     }
 }
 
 void FrameView::repaintFixedElementsAfterScrolling()
 {
     // For fixed position elements, update widget positions and compositing layers after scrolling,
     // but only if we're not inside of layout.
     if (!m_nestedLayoutCount && hasViewportConstrainedObjects()) {
         if (RenderView* renderView = this->renderView()) {
             renderView->updateWidgetPositions();
@@ skipping 1888 matching lines @@
 }
     
 AXObjectCache* FrameView::axObjectCache() const
 {
     if (frame() && frame()->document())
         return frame()->document()->existingAXObjectCache();
     return 0;
 }
     
 } // namespace WebCore