Remove opaque alpha channel special case

third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp

Index: third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
index 5ee289a40e3ca26c6604984daf57cd59664b3c46..ca5cd381ab7d136bddbcee7da9317cfe7f01229f 100644
--- a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp
@@ -159,7 +159,6 @@ bool GIFImageDecoder::HaveDecodedRow(size_t frame_index,
         *current_address = color_table_iter[source_value];
       } else {
         *current_address = 0;
-        current_buffer_saw_alpha_ = true;
       }
     }
   } else {
@@ -168,8 +167,6 @@ bool GIFImageDecoder::HaveDecodedRow(size_t frame_index,
       if ((source_value != transparent_pixel) &&
           (source_value < color_table.size()))
         *current_address = color_table_iter[source_value];
-      else
-        current_buffer_saw_alpha_ = true;
     }
   }
 
@@ -191,10 +188,13 @@ bool GIFImageDecoder::FrameComplete(size_t frame_index) {
   if (!InitFrameBuffer(frame_index))
     return SetFailed();
 
-  if (!current_buffer_saw_alpha_)
-    CorrectAlphaWhenFrameBufferSawNoAlpha(frame_index);
+  ImageFrame& buffer = frame_buffer_cache_[frame_index];
+
+  const GIFFrameContext* frame_context = reader_->frameContext(frame_index);
+  const size_t transparent_pixel = frame_context->transparentPixel();
+  buffer.SetHasAlpha(transparent_pixel != kNotFound);

[scroggo_chromium, 2017/05/08 14:56:36]

I think we should also consider the case where the transparent pixel is outside
the range of its ColorMap (which may be either the local or global one).

[cblume, 2017/05/25 07:47:04]

Done.

 
-  frame_buffer_cache_[frame_index].SetStatus(ImageFrame::kFrameComplete);
+  buffer.SetStatus(ImageFrame::kFrameComplete);
 
   return true;
 }
@@ -269,10 +269,6 @@ void GIFImageDecoder::Parse(GIFParseQuery query) {
     SetFailed();
 }
 
-void GIFImageDecoder::OnInitFrameBuffer(size_t frame_index) {
-  current_buffer_saw_alpha_ = false;
-}
-
 bool GIFImageDecoder::CanReusePreviousFrameBuffer(size_t frame_index) const {
   DCHECK(frame_index < frame_buffer_cache_.size());
   return frame_buffer_cache_[frame_index].GetDisposalMethod() !=