Oilpan: fix build after r197805.

Source/core/paint/NinePieceImageGridTest.cpp

Index: Source/core/paint/NinePieceImageGridTest.cpp
diff --git a/Source/core/paint/NinePieceImageGridTest.cpp b/Source/core/paint/NinePieceImageGridTest.cpp
index 3c8ae95951a7e6b270d4d18e289c4f250585bed7..9b8e440bb704521ff416c1a543b325f88d37ce28 100644
--- a/Source/core/paint/NinePieceImageGridTest.cpp
+++ b/Source/core/paint/NinePieceImageGridTest.cpp
@@ -21,7 +21,7 @@ public:
 
     PassRefPtr<StyleImage> generatedImage()
     {
-        RefPtr<CSSLinearGradientValue> gradient = CSSLinearGradientValue::create(Repeating);
+        RefPtrWillBeRawPtr<CSSLinearGradientValue> gradient = CSSLinearGradientValue::create(Repeating);
         RefPtr<StyleGeneratedImage> image = StyleGeneratedImage::create(gradient.get());
         return image;
     }
@@ -268,4 +268,3 @@ TEST_F(NinePieceImageGridTest, NinePieceImagePainting)
 
 } // namespace
 } // namespace blink
-