Avoid using forced layout to trigger paint invalidation for SVG containers

third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2009 Google, Inc.  All rights reserved.
  * Copyright (C) 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 52 matching lines @@
     void layout() override;
 
     void addChild(LayoutObject* child, LayoutObject* beforeChild = nullptr) final;
     void removeChild(LayoutObject*) final;
     void addOutlineRects(Vector<LayoutRect>&, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot) const final;
 
     FloatRect strokeBoundingBox() const final { return m_strokeBoundingBox; }
 
     bool nodeAtFloatPoint(HitTestResult&, const FloatPoint& pointInParent, HitTestAction) override;
 
+    enum TransformChangeFlags {

[pdr., 2016/06/15 12:15:17]

Returning just ScaleChange from LayoutSVGResourceMarker::calculateLocalTransform
might introduce bugs because the TransformChange bit will be 0.

WDYT about switching the logic and renaming ScaleChange to
ScaleKnownToBeUnchanged?

[fs, 2016/06/15 22:10:33]

Yes, not too happy about this bit (no pun intended). Returning a "negative" bit
might work for now. 

[fs, 2016/06/20 11:48:49]

Rewrote it to use an (ordered) enumeration instead. Maybe a little better, WDYT?
PTAL.

+        NoTransformChange = 0,
+        TransformChange = 1u << 0,
+        ScaleChange = 1u << 1,
+    };
     // Allow LayoutSVGTransformableContainer to hook in at the right time in layout().
-    virtual bool calculateLocalTransform() { return false; }
+    virtual unsigned calculateLocalTransform() { return NoTransformChange; }
 
     // Allow LayoutSVGViewportContainer to hook in at the right times in layout() and nodeAtFloatPoint().
     virtual void calcViewport() { }
     virtual bool pointIsInsideViewportClip(const FloatPoint& /*pointInParent*/) { return true; }
 
     virtual void determineIfLayoutSizeChanged() { }
 
     void updateCachedBoundaries();
 
     void descendantIsolationRequirementsChanged(DescendantIsolationState) final;
@@ skipping 10 matching lines @@
     bool m_didScreenScaleFactorChange : 1;
     mutable bool m_hasNonIsolatedBlendingDescendants : 1;
     mutable bool m_hasNonIsolatedBlendingDescendantsDirty : 1;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutSVGContainer, isSVGContainer());
 
 } // namespace blink
 
 #endif // LayoutSVGContainer_h