[pdf] Have DM set producer

The default PDF producer string includes the Skia milestone number,
making them change every time the milestone is updated. Avoid this when
running DM.

Change-Id: I96dcd18fe0a5c9f7f4fd5c6e092e57b30c0d28ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/864917
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 032ef69..0695bfd6 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -1998,6 +1998,7 @@
     metadata.fTitle = src.name();
     metadata.fSubject = "rendering correctness test";
     metadata.fCreator = "Skia/DM";
+    metadata.fProducer = "Skia/PDF HEAD"; // Set producer to avoid SK_MILESTONE churn.
     metadata.fRasterDPI = fRasterDpi;
     metadata.fPDFA = fPDFA;