Fix PDF printing for mixed page sizes and annotations.

PDF contents have to be fit into the printable area before the PDF gets
flattened for printing. Otherwise some PDFs will not print correctly.
r554188 flipped the ordering, so this flips it back.

BUG=873840

Change-Id: I68a05d0951caa31080b3b9bb424d458a899b92a7
Reviewed-on: https://chromium-review.googlesource.com/1237719Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593258}

pdf/pdfium/pdfium_print.cc

@@ -331,18 +331,16 @@ pp::Buffer_Dev PDFiumPrint::PrintPagesAsPDF(
     return pp::Buffer_Dev();
   }
 
-  // Now flatten all the output pages.
-  if (!FlattenPrintData(output_doc.get()))
-    return pp::Buffer_Dev();
-
   pp::Buffer_Dev buffer;
   uint32_t pages_per_sheet = pdf_print_settings.pages_per_sheet;
   uint32_t scale_factor = pdf_print_settings.scale_factor;
   if (ShouldDoNup(pages_per_sheet)) {
+    if (FlattenPrintData(output_doc.get()))
       buffer = NupPdfToPdf(output_doc.get(), pages_per_sheet, print_settings);
   } else {
     FitContentsToPrintableAreaIfRequired(output_doc.get(),
                                          scale_factor / 100.0f, print_settings);
+    if (FlattenPrintData(output_doc.get()))
       buffer = GetPrintData(output_doc.get());
   }