Sky: Add a DrawLooper interface to the painting API to be used for shadows.

sky/engine/core/painting/Paint.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKY_ENGINE_CORE_PAINTING_PAINT_H_
 #define SKY_ENGINE_CORE_PAINTING_PAINT_H_
 
 #include "sky/engine/tonic/dart_wrappable.h"
 #include "sky/engine/wtf/PassRefPtr.h"
 #include "sky/engine/wtf/RefCounted.h"
 #include "third_party/skia/include/core/SkPaint.h"
 
 namespace blink {
 
+class DrawLooper;
+
 class Paint : public RefCounted<Paint>, public DartWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
     ~Paint() override;
     static PassRefPtr<Paint> create()
     {
         return adoptRef(new Paint);
     }
+    static PassRefPtr<Paint> createWithWeakRef(SkPaint* paint)
+    {
+        return adoptRef(new Paint(paint));
+    }

[abarth-chromium, 2015/05/27 02:12:51]

How does this work?  It seems like the Paint object can live for an arbitrary
period of time but the SkPaint object passed in here will die at some point. 
After the SkPaint dies, won't the Paint object point to unallocated memory?

[Matt Perry, 2015/05/27 14:46:32]

Yeah, I'm using it with SkLayerDrawLooper::Builder::addLayerOnTop. The
documentation for this method says it "returns a paint you can modify, but that
ptr is only valid until the next call made to addLayer()."

The way I'm handling this lifetime issue is by handing this Paint object to a
callback, and only guaranteeing that it's valid while the callback runs. (See
LayerDrawLooperBuilder::addLayerOnTop).

 
-    bool isAntiAlias() const { return m_paint.isAntiAlias(); }
-    void setIsAntiAlias(bool value) { m_paint.setAntiAlias(value); }
+    bool isAntiAlias() const { return m_paint->isAntiAlias(); }
+    void setIsAntiAlias(bool value) { m_paint->setAntiAlias(value); }
 
-    unsigned color() const { return m_paint.getColor(); }
-    void setColor(unsigned color) { m_paint.setColor(color); }
+    unsigned color() const { return m_paint->getColor(); }
+    void setColor(unsigned color) { m_paint->setColor(color); }
 
     void setARGB(unsigned a, unsigned r, unsigned g, unsigned b)
     {
-        m_paint.setARGB(a, r, g, b);
+        m_paint->setARGB(a, r, g, b);
     }
+    void setDrawLooper(DrawLooper* looper);
 
-    const SkPaint& paint() const { return m_paint; }
+    const SkPaint& paint() const { return *m_paint; }
 
 private:
     Paint();
+    Paint(SkPaint* paint);
 
-    SkPaint m_paint;
+    SkPaint* m_paint;
+
+    // The backing for m_paint when we own the SkPaint. Not used when
+    // constructed with createWithWeakRef.
+    SkPaint m_inline_paint;
 };
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_PAINTING_PAINT_H_