SkPDF: SkPDFDocument reorganized so that some objects can be serialized early.

tests/PDFDocumentTest.cpp

Index: tests/PDFDocumentTest.cpp
diff --git a/tests/PDFDocumentTest.cpp b/tests/PDFDocumentTest.cpp
index 995e35f8c0381b9ca1881cd827c156e4e846c0ad..98d1864df1d4cea18cf4397d12fe54dc43403990 100644
--- a/tests/PDFDocumentTest.cpp
+++ b/tests/PDFDocumentTest.cpp
@@ -33,7 +33,8 @@ static void test_abort(skiatest::Reporter* reporter) {
 
     doc->abort();
 
-    REPORTER_ASSERT(reporter, stream.bytesWritten() == 0);
+    // Test that only the header is written, not the full document.
+    REPORTER_ASSERT(reporter, stream.bytesWritten() < 256);
 }
 
 static void test_abortWithFile(skiatest::Reporter* reporter) {