Early reporting of opaqueness by decoders.

third_party/WebKit/Source/platform/image-decoders/jpeg/JPEGImageDecoder.cpp

Index: third_party/WebKit/Source/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/jpeg/JPEGImageDecoder.cpp b/third_party/WebKit/Source/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
index a89c388b078d78d3507ebafda4a17ee1aa95f2d6..4e7f1002f9cbeb07d64e9cc82ae72395af599d61 100644
--- a/third_party/WebKit/Source/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/jpeg/JPEGImageDecoder.cpp
@@ -753,6 +753,13 @@ size_t JPEGImageDecoder::decodedYUVWidthBytes(int component) const
     return computeYUVWidthBytes(info, component);
 }
 
+bool JPEGImageDecoder::frameHasAlphaAtIndex(size_t index) const
+{
+    if (index == 0 && isAllDataReceived())

[scroggo_chromium, 2016/05/16 20:38:20]

I don't think this is quite correct. It's possible we've received all the data,
but the stream is truncated, so the frame is not complete, thus it has
transparency at the bottom.

+        return false;
+    return ImageDecoder::frameHasAlphaAtIndex(index);
+}
+
 unsigned JPEGImageDecoder::desiredScaleNumerator() const
 {
     size_t originalBytes = size().width() * size().height() * 4;