Change GraphicsContext::createCompatibleBuffer to return something non-null

Source/platform/graphics/CrossfadeGeneratedImage.cpp

Index: Source/platform/graphics/CrossfadeGeneratedImage.cpp
diff --git a/Source/platform/graphics/CrossfadeGeneratedImage.cpp b/Source/platform/graphics/CrossfadeGeneratedImage.cpp
index 667e2553eccb0d74cebcd8306a3e526a1b00abd2..5cc3b17cbef67556680a60fa153b8a63d0ee2168 100644
--- a/Source/platform/graphics/CrossfadeGeneratedImage.cpp
+++ b/Source/platform/graphics/CrossfadeGeneratedImage.cpp
@@ -99,7 +99,7 @@ void CrossfadeGeneratedImage::draw(GraphicsContext* context, const FloatRect& ds
 
 void CrossfadeGeneratedImage::drawPattern(GraphicsContext* context, const FloatRect& srcRect, const FloatSize& scale, const FloatPoint& phase, CompositeOperator compositeOp, const FloatRect& dstRect, blink::WebBlendMode blendMode, const IntSize& repeatSpacing)
 {
-    OwnPtr<ImageBuffer> imageBuffer = context->createCompatibleBuffer(m_size);
+    OwnPtr<ImageBuffer> imageBuffer = context->createRasterBuffer(m_size);
     if (!imageBuffer)
         return;