Use SkLayerDrawLooper::Builder to construct SkLayerDrawLooper.

Source/platform/graphics/DrawLooper.h

Index: Source/platform/graphics/DrawLooper.h
diff --git a/Source/platform/graphics/DrawLooper.h b/Source/platform/graphics/DrawLooper.h
index 4a66910c30029162ca8768a7cc52f49b3dc366f8..521dd6e1a461c7285c1aee767116690be43ef3d5 100644
--- a/Source/platform/graphics/DrawLooper.h
+++ b/Source/platform/graphics/DrawLooper.h
@@ -32,18 +32,19 @@
 #define DrawLooper_h
 
 #include "platform/PlatformExport.h"
+#include "third_party/skia/include/effects/SkLayerDrawLooper.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 
 class SkDrawLooper;
-class SkLayerDrawLooper;
 
 namespace WebCore {
 
 class Color;
 class FloatSize;
 
-class PLATFORM_EXPORT DrawLooper {
+class PLATFORM_EXPORT DrawLooper : public RefCounted<DrawLooper> {

[jbroman, 2014/02/24 17:47:44]

Why make this refcounted? The second level of refcounting seems redundant here,
especially now that this class is totally immutable.

(In fact, we might be able to remove the WTF_MAKE_NONCOPYABLE.)

[Dominik Grewe, 2014/02/24 18:11:57]

If I remove it the compiler complains that it can't call deref() on DrawLooper.

[jbroman, 2014/02/24 18:18:53]

If you make this class not refcounted, you have to use
OwnPtr/PassOwnPtr/adoptPtr (which manages single-owner semantics) instead of
RefPtr/PassRefPtr/adoptRef to hold pointers to it.

[Dominik Grewe, 2014/02/24 18:34:39]

Done.

     // Implementing the copy constructor properly would require writing code to
     // copy the underlying SkDrawLooper.
     WTF_MAKE_NONCOPYABLE(DrawLooper);
@@ -58,20 +59,33 @@ public:
         ShadowIgnoresAlpha
     };
 
-    DrawLooper();
     ~DrawLooper();
 
     // Callees should not modify this looper other than to iterate over it.
     // A downcast to SkLayerDrawLooper* is tantamount to a const_cast.
     SkDrawLooper* skDrawLooper() const;
 
-    void addUnmodifiedContent();
-    void addShadow(const FloatSize& offset, float blur, const Color&,
-        ShadowTransformMode = ShadowRespectsTransforms,
-        ShadowAlphaMode = ShadowRespectsAlpha);
+    class Builder {
+    public:
+        Builder() { }
+        ~Builder() { }
+
+        void addUnmodifiedContent();
+        void addShadow(const FloatSize& offset, float blur, const Color&,
+            ShadowTransformMode = ShadowRespectsTransforms,
+            ShadowAlphaMode = ShadowRespectsAlpha);
+
+        // Pass layers to new DrawLooper object and return it. The builder
+        // should not be used any more after calling this method.
+        PassRefPtr<DrawLooper> detachDrawLooper();
+
+    private:
+        SkLayerDrawLooper::Builder m_skDrawLooperBuilder;
+    };
 
 private:
-    RefPtr<SkLayerDrawLooper> m_skDrawLooper;
+    DrawLooper(SkDrawLooper*);
+    RefPtr<SkDrawLooper> m_skDrawLooper;
 };
 
 } // namespace WebCore