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

ui/gfx/codec/png_codec_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
 #include <cmath>
 
@@ skipping 1155 matching lines @@
 
   // encode
   std::vector<unsigned char> encoded_normal;
   EXPECT_TRUE(
       PNGCodec::EncodeBGRASkBitmap(original_bitmap, false, &encoded_normal));
 
   std::vector<unsigned char> encoded_fast;
   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;
   EXPECT_TRUE(
       PNGCodec::Decode(&encoded_normal[0], encoded_normal.size(), &decoded));
   EXPECT_TRUE(BitmapsAreEqual(decoded, original_bitmap));
 
   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));
 }
 
 
 }  // namespace gfx