The libpng patch had some missing ifdefs that went unnoticed because …

…the patch itself was broken, so those bits were never applied. This caused problems on Mac, where we had libpng < 1.5. Fix up the patch to add the necessary ifdefs and use the old code if we have libpng < 1.5

patches/chromium_libpng_1.5.patch

@@ -27,14 +27,19 @@ Index: third_party/WebKit/Source/WebCore/platform/image-decoders/png/PNGImageDec
          ColorProfile colorProfile;
          colorProfile.append(profile, profileLength);
          return colorProfile;
-@@ -241,11 +245,11 @@
+@@ -241,11 +245,16 @@
  {
      png_structp png = m_reader->pngPtr();
      png_infop info = m_reader->infoPtr();
 -    png_uint_32 width = png->width;
 -    png_uint_32 height = png->height;
++#if PNG_LIBPNG_VER_MAJOR >= 1 && PNG_LIBPNG_VER_MINOR >= 5
 +    png_uint_32 width = png_get_image_width(png, info);
 +    png_uint_32 height = png_get_image_height(png, info);
++#else
++    png_uint_32 width = png->width;
++    png_uint_32 height = png->height;
++#endif
 
      // Protect against large images.
 -    if (png->width > cMaxPNGSize || png->height > cMaxPNGSize) {
@@ -55,13 +60,17 @@ Index: third_party/WebKit/Source/WebCore/platform/image-decoders/png/PNGImageDec
      }
  }
 
-@@ -343,7 +351,8 @@
+@@ -343,6 +351,11 @@
          // For PNGs, the frame always fills the entire image.
          buffer.setOriginalFrameRect(IntRect(IntPoint(), size()));
 
 -        if (m_reader->pngPtr()->interlaced)
++#if PNG_LIBPNG_VER_MAJOR >= 1 && PNG_LIBPNG_VER_MINOR >= 5
 +        if (png_get_interlace_type(m_reader->pngPtr(), m_reader->infoPtr())
 +		!= PNG_INTERLACE_NONE)
++#else
++        if (m_reader->pngPtr()->interlaced)
++#endif
              m_reader->createInterlaceBuffer((m_reader->hasAlpha() ? 4 : 3) * size().width() * size().height());
      }