DM: PDFSink sets rasterizer keyword

Review URL: https://codereview.chromium.org/1376573002
diff --git a/dm/DMSrcSink.h b/dm/DMSrcSink.h
index 9e0ef49..d881137 100644
--- a/dm/DMSrcSink.h
+++ b/dm/DMSrcSink.h
@@ -213,12 +213,14 @@
 
 class PDFSink : public Sink {
 public:
-    PDFSink();
+    PDFSink(const char* rasterizer);
 
     Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
     int enclave() const override { return kAnyThread_Enclave; }
     const char* fileExtension() const override { return "pdf"; }
     SinkFlags flags() const override { return SinkFlags{ SinkFlags::kVector, SinkFlags::kDirect }; }
+private:
+    const char* fRasterizer;
 };
 
 class XPSSink : public Sink {