GN: add sources_when_disabled to optional

tools/fiddle/fiddle_main.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include "SkForceLinking.h"
@@ skipping 118 matching lines @@
                 exit(1);
             }
             srand(0);
             draw(surface->getCanvas());
             gpuData.reset(encode_snapshot(surface));
         }
     }
     if (options.pdf) {
         SkDynamicMemoryWStream pdfStream;
         sk_sp<SkDocument> document(SkDocument::MakePDF(&pdfStream));
-        srand(0);
-        draw(document->beginPage(options.size.width(), options.size.height()));
-        document->close();
-        pdfData.reset(pdfStream.copyToData());
+        if (document) {
+            srand(0);
+            draw(document->beginPage(options.size.width(), options.size.height()));
+            document->close();
+            pdfData.reset(pdfStream.copyToData());
+        }
     }
     if (options.skp) {
         SkSize size;
         size = options.size;
         SkPictureRecorder recorder;
         srand(0);
         draw(recorder.beginRecording(size.width(), size.height()));
         auto picture = recorder.finishRecordingAsPicture();
         SkDynamicMemoryWStream skpStream;
         picture->serialize(&skpStream);
         skpData.reset(skpStream.copyToData());
     }
 
     printf("{\n");
     dump_output(rasterData, "Raster", !gpuData && !pdfData && !skpData);
     dump_output(gpuData, "Gpu", !pdfData && !skpData);
     dump_output(pdfData, "Pdf", !skpData);
     dump_output(skpData, "Skp");
     printf("}\n");
 
     return 0;
 }