Use RefPtr to manage shaders in Gradient and Pattern.

Source/core/platform/graphics/Pattern.h

Index: Source/core/platform/graphics/Pattern.h
diff --git a/Source/core/platform/graphics/Pattern.h b/Source/core/platform/graphics/Pattern.h
index ef361521c3129bb379c1591cb2712013834a64d3..12cec68e51f024d59e2df43f0e061695f03d2c5d 100644
--- a/Source/core/platform/graphics/Pattern.h
+++ b/Source/core/platform/graphics/Pattern.h
@@ -47,7 +47,7 @@ public:
     {
         return adoptRef(new Pattern(tileImage, repeatX, repeatY));
     }
-    virtual ~Pattern();
+    ~Pattern();
 
     Image* tileImage() const { return m_tileImage.get(); }
 
@@ -66,7 +66,7 @@ private:
     bool m_repeatX;
     bool m_repeatY;
     AffineTransform m_patternSpaceTransformation;
-    SkShader* m_pattern;
+    RefPtr<SkShader> m_pattern;
     int m_externalMemoryAllocated;
 };