SkDocument/PDF: new API

has a pdf/a switch.
sets metadata in factory.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1916093002

Review URL: https://codereview.chromium.org/1916093002
diff --git a/tests/PDFInvalidBitmapTest.cpp b/tests/PDFInvalidBitmapTest.cpp
index 57e51f0..c9685f7 100644
--- a/tests/PDFInvalidBitmapTest.cpp
+++ b/tests/PDFInvalidBitmapTest.cpp
@@ -45,7 +45,7 @@
 
 DEF_TEST(PDFInvalidBitmap, reporter) {
     SkDynamicMemoryWStream stream;
-    SkAutoTUnref<SkDocument> document(SkDocument::CreatePDF(&stream));
+    sk_sp<SkDocument> document(SkDocument::MakePDF(&stream));
     SkCanvas* canvas = document->beginPage(100, 100);
 
     canvas->drawBitmap(SkBitmap(), 0, 0);