Move toClipPath to SVGGeometryElement.

Source/core/svg/SVGUseElement.h

Index: Source/core/svg/SVGUseElement.h
diff --git a/Source/core/svg/SVGUseElement.h b/Source/core/svg/SVGUseElement.h
index 88f3537941989ef5e6577921cd4ddb4107c23f2d..cb44838e8a48ad6f10cbf9fdd43c4e3e206a5321 100644
--- a/Source/core/svg/SVGUseElement.h
+++ b/Source/core/svg/SVGUseElement.h
@@ -24,6 +24,7 @@
 #include "core/events/EventSender.h"
 #include "core/fetch/DocumentResource.h"
 #include "core/svg/SVGAnimatedLength.h"
+#include "core/svg/SVGGeometryElement.h"
 #include "core/svg/SVGGraphicsElement.h"
 #include "core/svg/SVGURIReference.h"
 #include "platform/heap/Handle.h"
@@ -43,7 +44,7 @@ public:
 
     void invalidateShadowTree();
 
-    LayoutObject* layoutObjectClipChild() const;
+    SVGGeometryElement* layoutObjectClipChild(Path&) const;

[pdr., 2015/06/09 05:15:58]

Sadness... the original code is worse than I expected and has real bugs. This
may require many patches and I understand if you'd like to work on something
else. If you're up for it, I'll sketch out a good first patch below:

SVGClipPainter::applyClippingToContext has two "modes":
1) A "path-only" approach (tryPathOnlyClipping) which calls
SVGUseElement::toClipPath
2) A mask approach (drawClipMaskContent) which ends up calling
SVGUseElement::layoutObjectClipChild
Our goal is to unify these so they use the same code. The following might be a
good design:

const SVGGraphicsElement* SVGUseElement::targetGraphicsElementForClipping();
You should write a comment in the header file describing what we are returning
and why. You may want to reference the spec, particularly this part: "If a <use>
element is a child of a clipPath element, it must directly reference <path>,
<text> or basic shapes elements." You probably want to actually check for the
allowed references too... something like isSVGTextElement() || isSVGTSpanElement
|| isSVGGeometryElement. You may also want to mention how we will return null if
an allowed element is not available.

Lets leave SVGUseElement::toClipPath for now, but make it non-virtual. Also
change the implementation to call our new targetGraphicsElementForClipping
function, but make sure to check isSVGGeometryElement because path-only clipping
doesn't work for text.

[hyunjunekim2, 2015/06/10 14:00:42]

I will try again for your advice.

 
     SVGAnimatedLength* x() const { return m_x.get(); }
     SVGAnimatedLength* y() const { return m_y.get(); }
@@ -71,7 +72,6 @@ private:
     virtual void svgAttributeChanged(const QualifiedName&) override;
 
     virtual LayoutObject* createLayoutObject(const ComputedStyle&) override;
-    virtual void toClipPath(Path&) override;
 
     void clearResourceReferences();
     void buildShadowAndInstanceTree(SVGElement* target);