SkPDF: add basic metadata support

dm/DMSrcSink.cpp

Index: dm/DMSrcSink.cpp
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 981e47d6c0bf84690c25c8a49392fa2e3abadc18..22e8961447f3d2e090f413dcfa48aecfce206ffc 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -929,6 +929,12 @@ Error PDFSink::draw(const Src& src, SkBitmap*, SkWStream* dst, SkString*) const
     if (!doc) {
         return "SkDocument::CreatePDF() returned nullptr";
     }
+    SkTArray<SkDocument::Attribute> info;
+    info.emplace_back(SkString("Title"), src.name());
+    info.emplace_back(SkString("Subject"),
+                      SkString("rendering correctness test"));
+    info.emplace_back(SkString("Creator"), SkString("Skia/DM"));
+    doc->setMetadata(info, nullptr, nullptr);
     return draw_skdocument(src, doc.get(), dst);
 }