DM: better SkDocument error message.

dm/DMSrcSink.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 "DMSrcSink.h"
 #include "SkAndroidCodec.h"
 #include "SkCodec.h"
@@ skipping 985 matching lines @@
     canvas->readPixels(dst, 0, 0);
     if (FLAGS_abandonGpuContext) {
         factory.abandonContexts();
     }
     return "";
 }
 
 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
 
 static Error draw_skdocument(const Src& src, SkDocument* doc, SkWStream* dst) {
-    // Print the given DM:Src to a document, breaking on 8.5x11 pages.
+    if (src.size().isEmpty()) {
+        return "Source has empty dimensions";
+    }
     SkASSERT(doc);
     int width  = src.size().width(),
         height = src.size().height();
 
     if (FLAGS_multiPage) {
+        // Print the given DM:Src to a document, breaking on 8.5x11 pages.
         const int kLetterWidth = 612,  // 8.5 * 72
                 kLetterHeight = 792;   // 11 * 72
         const SkRect letter = SkRect::MakeWH(SkIntToScalar(kLetterWidth),
                                              SkIntToScalar(kLetterHeight));
 
         int xPages = ((width - 1) / kLetterWidth) + 1;
         int yPages = ((height - 1) / kLetterHeight) + 1;
 
         for (int y = 0; y < yPages; ++y) {
             for (int x = 0; x < xPages; ++x) {
@@ skipping 470 matching lines @@
             skr.visit<void>(i, drawsAsSingletonPictures);
         }
         SkAutoTUnref<SkPicture> macroPic(macroRec.endRecordingAsPicture());
 
         canvas->drawPicture(macroPic);
         return check_against_reference(bitmap, src, fSink);
     });
 }
 
 }  // namespace DM