Add infrastructure for partial layouts

Source/core/page/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
@@ skipping 317 matching lines @@
     void setInProgrammaticScroll(bool programmaticScroll) { m_inProgrammaticScroll = programmaticScroll; }
 
     void setHasSoftwareFilters(bool hasSoftwareFilters) { m_hasSoftwareFilters = hasSoftwareFilters; }
     bool hasSoftwareFilters() const { return m_hasSoftwareFilters; }
 
     virtual bool isActive() const OVERRIDE;
 
     // DEPRECATED: Use viewportConstrainedVisibleContentRect() instead.
     IntSize scrollOffsetForFixedPosition() const;
 
+    bool shouldStopPartialLayout() const { return m_shouldStopPartialLayout; }
+    void checkPartialLayoutComplete(RenderObject*);
+    void setStopLayoutAtRenderer(RenderObject* renderer) { m_stopLayoutAtRenderer = renderer; }
+    void resetPartialLayoutState() { m_stopLayoutAtRenderer = 0; m_shouldStopPartialLayout = false; }

[esprehn, 2013/08/18 03:43:15]

Isn't shouldStopPartialLayout the same as checking if stopLayoutAtRenderer is
not null? Why do you need a boolean?

[pdr., 2013/08/20 06:19:10]

We need the boolean to track that we're exiting in the middle of layout.

m_stopLayoutAtRenderer is used to determine which renderer we need to stop
layout on.
m_shouldStopPartialLayout is used to say 'STOP' to all the layout methods.

In a full, complete layout, m_stopLayoutAtRenderer will be 0 and
m_shouldStopPartialLayout will be false.
In a partial layout, before we've laid out the target renderer,
m_shouldStopPartialLayout will be false.
In a partial layout, after we've laid out the target renderer,
m_shouldStopPartialLayout will be true.

Happy to update these names if we can make this more understandable. One idea is
to move this state into a small struct or class such as PartialLayoutState to
hide some of these details. We could also hide some kind of
temporarilyDisablePartialLayout functionality in a class for working around
two-pass layouts.

+
 protected:
     virtual bool scrollContentsFastPath(const IntSize& scrollDelta, const IntRect& rectToScroll, const IntRect& clipRect);
     virtual void scrollContentsSlowPath(const IntRect& updateRect);
 
     virtual bool isVerticalDocument() const;
     virtual bool isFlippedDocument() const;
 
 private:
     explicit FrameView(Frame*);
 
@@ skipping 171 matching lines @@
     OwnPtr<ViewportConstrainedObjectSet> m_viewportConstrainedObjects;
 
     static double s_normalDeferredRepaintDelay;
     static double s_initialDeferredRepaintDelayDuringLoading;
     static double s_maxDeferredRepaintDelayDuringLoading;
     static double s_deferredRepaintDelayIncrementDuringLoading;
 
     bool m_hasSoftwareFilters;
 
     float m_visibleContentScaleFactor;
+
+    bool m_shouldStopPartialLayout;
+    RenderObject* m_stopLayoutAtRenderer;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)
 {
     if (m_isVisuallyNonEmpty)
         return;
     m_visuallyNonEmptyCharacterCount += count;
     // Use a threshold value to prevent very small amounts of visible content from triggering didFirstVisuallyNonEmptyLayout.
     // The first few hundred characters rarely contain the interesting content of the page.
     static const unsigned visualCharacterThreshold = 200;
@@ skipping 33 matching lines @@
     ASSERT(!widget || widget->isFrameView());
     return static_cast<const FrameView*>(widget);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toFrameView(const FrameView*);
 
 } // namespace WebCore
 
 #endif // FrameView_h