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..90a8e173697ee8df04e2d0b821817ead629da3f9 100644
--- a/Source/platform/graphics/DrawLooper.h
+++ b/Source/platform/graphics/DrawLooper.h
@@ -32,11 +32,11 @@
 #define DrawLooper_h
 
 #include "platform/PlatformExport.h"
+#include "third_party/skia/include/effects/SkLayerDrawLooper.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/RefPtr.h"
 
 class SkDrawLooper;
-class SkLayerDrawLooper;
 
 namespace WebCore {
 
@@ -63,7 +63,7 @@ public:
 
     // 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;
+    SkDrawLooper* skDrawLooper();

[jbroman, 2014/02/24 15:23:33]

This method now destroys the WebCore::DrawLooper as well, and it's not at all
obvious that it has this effect. If, for example, a callee tried to keep a
DrawLooper instance around, this would not behave as one would expect.

I like that Skia is making draw loopers immutable, but I think the
platform/graphics/ API should make this clear. My suggestion would be to mirror
the change in the Skia API, and call this class "DrawLooperBuilder" or similar,
and rename this something that makes it obvious that it resets the builder, like
the method SkLayerDrawLooper::Builder has.

It could either return an SkDrawLooper* or a new WebCore::DrawLooper type (which
would be a simple wrapper if we don't want to expose Skia types to core/).

[Dominik Grewe, 2014/02/24 15:47:28]

Makes sense. How about replicating the structure in Skia, i.e. keep the
'DrawLooper' class but move all the add* methods to an inner 'Builder' class
with a 'detachLooper()' method?

 
     void addUnmodifiedContent();
     void addShadow(const FloatSize& offset, float blur, const Color&,
@@ -71,7 +71,7 @@ public:
         ShadowAlphaMode = ShadowRespectsAlpha);
 
 private:
-    RefPtr<SkLayerDrawLooper> m_skDrawLooper;
+    SkLayerDrawLooper::Builder m_skDrawLooperBuilder;
 };
 
 } // namespace WebCore