Fix retarded bitmath. << 8 != * 255

BUG=13360

Review URL: http://codereview.chromium.org/149164

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@20040 0039d316-1c4b-4281-b951-d872f2087c98

base/gfx/png_decoder.cc

@@ -329,10 +329,12 @@ bool PNGDecoder::Decode(const std::vector<unsigned char>* data,
     for (int i = width * height * 4 - 4; i >= 0; i -= 4) {
       unsigned char alpha = decoded_data[i + 3];
       if (alpha != 0 && alpha != 255) {
+        SkColor premultiplied = SkPreMultiplyARGB(alpha,
+            decoded_data[i], decoded_data[i + 1], decoded_data[i + 2]);
         bitmap_data[i + 3] = alpha;
-        bitmap_data[i] = (decoded_data[i] * alpha) >> 8;
-        bitmap_data[i + 1] = (decoded_data[i + 1] * alpha) >> 8;
-        bitmap_data[i + 2] = (decoded_data[i + 2] * alpha) >> 8;
+        bitmap_data[i] = SkColorGetR(premultiplied);
+        bitmap_data[i + 1] = SkColorGetG(premultiplied);
+        bitmap_data[i + 2] = SkColorGetB(premultiplied);
       } else {
         bitmap_data[i + 3] = alpha;
         bitmap_data[i] = decoded_data[i];

base/gfx/png_encoder.cc

@@ -7,6 +7,7 @@
 #include "base/logging.h"
 #include "base/scoped_ptr.h"
 #include "third_party/skia/include/core/SkBitmap.h"
+#include "third_party/skia/include/core/SkUnPreMultiply.h"
 
 extern "C" {
 #include "third_party/libpng/png.h"
@@ -214,9 +215,10 @@ bool PNGEncoder::EncodeBGRASkBitmap(const SkBitmap& input,
 
       int alpha = SkColorGetA(pixel);
       if (alpha != 0 && alpha != 255) {
-        divided[i + 0] = (SkColorGetR(pixel) << 8) / alpha;
-        divided[i + 1] = (SkColorGetG(pixel) << 8) / alpha;
-        divided[i + 2] = (SkColorGetB(pixel) << 8) / alpha;
+        SkColor unmultiplied = SkUnPreMultiply::PMColorToColor(pixel);
+        divided[i + 0] = SkColorGetR(unmultiplied);
+        divided[i + 1] = SkColorGetG(unmultiplied);
+        divided[i + 2] = SkColorGetB(unmultiplied);
         divided[i + 3] = alpha;
       } else {
         divided[i + 0] = SkColorGetR(pixel);