Fix for png encoding performance regressions (part 2)

third_party/libpng/libpng.gyp

Index: third_party/libpng/libpng.gyp
diff --git a/third_party/libpng/libpng.gyp b/third_party/libpng/libpng.gyp
index 3c42401baa89318fbe6fc7abf80284e1d8e50e85..c1015cabebecfa676a730ee35b37a0b40cb06b8f 100644
--- a/third_party/libpng/libpng.gyp
+++ b/third_party/libpng/libpng.gyp
@@ -51,6 +51,14 @@
         4267, # TODO(jschuh): http://crbug.com/167187
         4146, # Unary minus applied to unsigned type.
       ],
+      # This is a fix for png encoding performance regressions (crbug.com/619850).
+      'msvs_settings': {
+        'VCCLCompilerTool': {
+          'AdditionalOptions': [
+            '/O2',
+          ],
+        },
+      },
       'conditions': [
         # Disable ARM optimizations on IOS.  Can't find a way to get gyp to even try
         # to compile the optimization files.  This works fine on GN.