Remove DCHECKs in GetYUVSubsampling().

Do not DCHECK CanDecodeToYUV() is true in GetYUVSubsampling(), because
GetYUVSubsampling() is called by the hardware decoding code paths, not
by the decoding-to-YUV code paths.

Do not assert that the AVIF_PIXEL_FORMAT_YUV400 case is not reached,
because that is the YUV format of monochrome AVIF images.

Please refer to https://crrev.com/c/2327461.

Bug: 915972
Change-Id: Iced2abe0f86b0f407855c371dbf5e6abef561946
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2340071Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795387}

third_party/blink/renderer/platform/image-decoders/avif/avif_image_decoder.cc

@@ -534,7 +534,6 @@ bool AVIFImageDecoder::CanReusePreviousFrameBuffer(size_t index) const {
 }
 
 cc::YUVSubsampling AVIFImageDecoder::GetYUVSubsampling() const {
-  DCHECK(CanDecodeToYUV());
   switch (decoder_->image->yuvFormat) {
     case AVIF_PIXEL_FORMAT_YUV420:
       return cc::YUVSubsampling::k420;
@@ -543,6 +542,7 @@ cc::YUVSubsampling AVIFImageDecoder::GetYUVSubsampling() const {
     case AVIF_PIXEL_FORMAT_YUV444:
       return cc::YUVSubsampling::k444;
     case AVIF_PIXEL_FORMAT_YUV400:
+      return cc::YUVSubsampling::kUnknown;
     case AVIF_PIXEL_FORMAT_NONE:
       NOTREACHED();
       return cc::YUVSubsampling::kUnknown;

third_party/blink/renderer/platform/image-decoders/avif/avif_image_decoder_test.cc

@@ -733,11 +733,14 @@ TEST_P(StaticAVIFColorTests, InspectImage) {
   decoder->SetData(data.get(), true);
   EXPECT_EQ(1u, decoder->FrameCount());
   EXPECT_EQ(kAnimationNone, decoder->RepetitionCount());
+  EXPECT_EQ(param.bit_depth > 8, decoder->ImageIsHighBitDepth());
+  auto metadata = decoder->MakeMetadataForDecodeAcceleration();
+  EXPECT_EQ(cc::ImageType::kAVIF, metadata.image_type);
+  // TODO(wtc): Check metadata.yuv_subsampling.
   ImageFrame* frame = decoder->DecodeFrameBufferAtIndex(0);
   ASSERT_TRUE(frame);
   EXPECT_EQ(ImageFrame::kFrameComplete, frame->GetStatus());
   EXPECT_FALSE(decoder->Failed());
-  EXPECT_EQ(param.bit_depth > 8, decoder->ImageIsHighBitDepth());
   // TODO(ryoh): How should we treat imir(mirroring), irot(rotation) and
   // clap(cropping)?
   // EXPECT_EQ(xxxx, decoder->Orientation());