Tune down libpng in DM.

Timing `out/dm --src gm --config srgb -w foo` on my desktop,
   - wall time drops from 3.72 -> 2.17 seconds; and
   - CPU time drops from 64.9 -> 27.9 seconds.

So again, close to 2x speedup.
(In exchange, the .pngs of our GMs grow from 57M to 73M.)

Change-Id: I6e2e8c8bda6371e857c8db41ca3119402a9056ae
Reviewed-on: https://skia-review.googlesource.com/16000
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/dm/DM.cpp b/dm/DM.cpp
index 6c8daf9b8c..aa2b081fb1 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -1033,6 +1033,8 @@ static bool dump_png(SkBitmap bitmap, const char* path, const char* md5) {
     png_set_IHDR(png, info, (png_uint_32)w, (png_uint_32)h, 8,
                  PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
                  PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+    png_set_filter(png,  PNG_FILTER_TYPE_BASE, PNG_FILTER_NONE);
+    png_set_compression_level(png, 1);
     png_write_info(png, info);
     for (int j = 0; j < h; j++) {
         png_bytep row = (png_bytep)(rgba + w*j);