Fix performance regression in png encoding caused by libpng update

third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp

Index: third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp b/third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp
index cfaae3f159f23f773b9a2b2a62cf7b69dbd47bc1..3553da1552c57dc8a4356ab00f1b12e1394a279f 100644
--- a/third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp
+++ b/third_party/WebKit/Source/platform/image-encoders/PNGImageEncoder.cpp
@@ -33,6 +33,8 @@
 #include "platform/graphics/ImageBuffer.h"
 #include "wtf/OwnPtr.h"
 
+#include "zlib.h"
+
 namespace blink {
 
 PNGImageEncoderState::~PNGImageEncoderState()
@@ -59,14 +61,19 @@ PassOwnPtr<PNGImageEncoderState> PNGImageEncoderState::create(const IntSize& ima
 
     // Optimize compression for speed.
     // The parameters are the same as what libpng uses by default for RGB and RGBA images, except:
-    // - the zlib compression level is 3 instead of 6, to avoid the lazy Ziv-Lempel match searching;
-    // - the delta filter is 1 ("sub") instead of 5 ("all"), to reduce the filter computations.
-    // The zlib memory level (8) and strategy (Z_FILTERED) will be set inside libpng.
-    //
+    // The zlib compression level is set to 3 instead of 6, to avoid the lazy Ziv-Lempel match searching.
+    png_set_compression_level(png, 3);
+
+    // The zlib memory level is set to 8.  This actually matches the default, we are just future-proofing.
+    png_set_compression_mem_level(png, 8);
+
+    // The zlib strategy is set to Z_FILTERED, which does not match the default.
     // Avoid the zlib strategies Z_HUFFMAN_ONLY or Z_RLE.
     // Although they are the fastest for poorly-compressible images (e.g. photographs),
     // they are very slow for highly-compressible images (e.g. text, drawings or business graphics)
-    png_set_compression_level(png, 3);
+    png_set_compression_strategy(png, Z_FILTERED);
+
+    // The delta filter is PNG_FILTER_SUB instead of PNG_ALL_FILTERS, to reduce the filter computations.
     png_set_filter(png, PNG_FILTER_TYPE_BASE, PNG_FILTER_SUB);
 
     png_set_write_fn(png, output, writeOutput, 0);