Separate and update PDF_DIFF_TRACE_IN_PNG

experimental/PdfViewer/SkPdfConfig.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPdfConfig_DEFINED
 #define SkPdfConfig_DEFINED
 
@@ skipping 13 matching lines @@
 
 // At various points in code we show the value of important variables with this flag
 //#define PDF_TRACE
 
 // displays the result of each read token, individual result
 //#define PDF_TRACE_READ_TOKEN
 
 // Every drawtext draws before a rectangle, in this way we see the one that might have failed
 //#define PDF_TRACE_DRAWTEXT
 
-// For each render operations, it will dump the canvas in a png
+// For each render operation, the canvas will be drawn to a png named
+// "/tmp/log_step_by_step/step-%i-%s.png"
 //#define PDF_TRACE_DIFF_IN_PNG
 
 // Does not clip at all, can be used in debugging issues
 //#define PDF_DEBUG_NO_CLIPING
 
 // Does not click the page, use is with 3x
 //#define PDF_DEBUG_NO_PAGE_CLIPING
 
 // render the page 3X bigger (with content in center) - used to make sure we don't mess up
 // positioning
@@ skipping 51 matching lines @@
 #ifdef PDF_TRACK_STREAM_OFFSETS
 struct SkPdfInputStreamRange {
     SkPdfInputStream fInputStream;
     const unsigned char* fRangeStart;
     const unsigned char* fRangeEnd;
 };
 #endif  //  PDF_TRACK_STREAM_OFFSETS
 
 
 #endif  // SkPdfConfig_DEFINED