Refactoring DrawLooper so that it can apply shadow effects as skia image filters

Source/core/platform/graphics/GraphicsContext.h

Index: Source/core/platform/graphics/GraphicsContext.h
diff --git a/Source/core/platform/graphics/GraphicsContext.h b/Source/core/platform/graphics/GraphicsContext.h
index 0dc1fc52d60e4db81e6523296257278c041fec1b..dcc806d8ee901f639b3be6bb32be0df8718b4f84 100644
--- a/Source/core/platform/graphics/GraphicsContext.h
+++ b/Source/core/platform/graphics/GraphicsContext.h
@@ -128,7 +128,7 @@ public:
     void setFillGradient(PassRefPtr<Gradient>);
     Gradient* fillGradient() const { return m_state->m_fillGradient.get(); }
 
-    SkDrawLooper* drawLooper() const { return m_state->m_looper.get(); }
+    DrawLooper* drawLooper() const { return m_state->m_looper.get(); }
     SkColor effectiveStrokeColor() const { return m_state->applyAlpha(m_state->m_strokeData.color().rgb()); }
 
     int getNormalizedAlpha() const;
@@ -303,7 +303,7 @@ public:
 
     // It is assumed that this draw looper is used only for shadows
     // (i.e. a draw looper is set if and only if there is a shadow).
-    void setDrawLooper(const DrawLooper&);
+    void setDrawLooper(PassRefPtr<DrawLooper>);
     void clearDrawLooper();
 
     void drawFocusRing(const Vector<IntRect>&, int width, int offset, const Color&);