Tweak libpng encoding parameters to increase speed on very large images.

ui/gfx/codec/png_codec_unittest.cc

Index: ui/gfx/codec/png_codec_unittest.cc
diff --git a/ui/gfx/codec/png_codec_unittest.cc b/ui/gfx/codec/png_codec_unittest.cc
index b0d1e3de40e98c3dbee5e956c57ef9d93130c065..eaada742fc1e91960e9997341e34c68419a9a9b2 100644
--- a/ui/gfx/codec/png_codec_unittest.cc
+++ b/ui/gfx/codec/png_codec_unittest.cc
@@ -1173,9 +1173,14 @@ TEST(PNGCodec, EncodeDecodeWithVaryingCompressionLevels) {
   EXPECT_TRUE(
       PNGCodec::FastEncodeBGRASkBitmap(original_bitmap, false, &encoded_fast));
 
+  std::vector<unsigned char> encoded_no_compress;
+  EXPECT_TRUE(PNGCodec::FastEncodeBGRASkBitmap(original_bitmap, false,
+                                               &encoded_no_compress));
+
   // Make sure the different compression settings actually do something; the
   // sizes should be different.
-  EXPECT_NE(encoded_normal.size(), encoded_fast.size());
+  EXPECT_GT(encoded_normal.size(), encoded_fast.size());
+  EXPECT_GT(encoded_fast.size(), encoded_no_compress.size());
 
   // decode, they should be identical to the original.
   SkBitmap decoded;
@@ -1186,6 +1191,10 @@ TEST(PNGCodec, EncodeDecodeWithVaryingCompressionLevels) {
   EXPECT_TRUE(
       PNGCodec::Decode(&encoded_fast[0], encoded_fast.size(), &decoded));
   EXPECT_TRUE(BitmapsAreEqual(decoded, original_bitmap));
+
+  EXPECT_TRUE(PNGCodec::Decode(&encoded_no_compress[0],
+                               encoded_no_compress.size(), &decoded));
+  EXPECT_TRUE(BitmapsAreEqual(decoded, original_bitmap));
 }