Separate and update PDF_DIFF_TRACE_IN_PNG

experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.h

Index: experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.h
diff --git a/experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.h b/experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.h
index 8ed354cfa138a8fe08f32f461ed0f16fb1733695..79b070f12ea0c182f58d0efd18a47a7e87490fa3 100644
--- a/experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.h
+++ b/experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.h
@@ -165,7 +165,10 @@ public:
     virtual ~SkPdfNativeTokenizer();
 
     // Reads one token. Returns false if there are no more tokens.
-    bool readToken(PdfToken* token);
+    // If writeDiff is true, and a token was read, create a PNG highlighting
+    // the difference caused by this command in /tmp/log_step_by_step.
+    // If PDF_TRACE_DIFF_IN_PNG is not defined, writeDiff does nothing.
+    bool readToken(PdfToken* token, bool writeDiff = false);
 
     // Put back a token to be read in the nextToken read. Only one token is allowed to be put
     // back. Must not necesaarely be the last token read.