LibGfx+LibVideo: Make BooleanDecoder usable for both VP8 and VP9

The marker bit is VP9-only, so move that into a new initialize_vp9()
function.

finish_decode() is VP9-only, so rename that to finish_decode_vp9().

Userland/Libraries/LibGfx/ImageFormats/BooleanDecoder.cpp

@@ -11,14 +11,19 @@
 
 namespace Gfx {
 
-/* 9.2.1 */
 ErrorOr<BooleanDecoder> BooleanDecoder::initialize(MaybeOwned<BigEndianInputBitStream> bit_stream, size_t size_in_bytes)
 {
     VERIFY(bit_stream->is_aligned_to_byte_boundary());
     auto value = TRY(bit_stream->read_value<u8>());
     u8 range = 255;
     u64 bits_left = (8 * size_in_bytes) - 8;
-    BooleanDecoder decoder { move(bit_stream), value, range, bits_left };
+    return BooleanDecoder { move(bit_stream), value, range, bits_left };
+}
+
+/* 9.2.1 */
+ErrorOr<BooleanDecoder> BooleanDecoder::initialize_vp9(MaybeOwned<BigEndianInputBitStream> bit_stream, size_t size_in_bytes)
+{
+    BooleanDecoder decoder = TRY(initialize(move(bit_stream), size_in_bytes));
     if (TRY(decoder.read_bool(128)))
         return Error::from_string_literal("Range decoder marker was non-zero");
     return decoder;
@@ -63,7 +68,7 @@ ErrorOr<u8> BooleanDecoder::read_literal(u8 bits)
 }
 
 /* 9.2.3 */
-ErrorOr<void> BooleanDecoder::finish_decode()
+ErrorOr<void> BooleanDecoder::finish_decode_vp9()
 {
     while (m_bits_left > 0) {
         auto padding_read_size = min(m_bits_left, 64);

Userland/Libraries/LibGfx/ImageFormats/BooleanDecoder.h

@@ -14,13 +14,18 @@
 
 namespace Gfx {
 
+// Can decode bitstreams encoded with VP8's and VP9's arithmetic boolean encoder.
 class BooleanDecoder {
 public:
-    /* (9.2) */
     static ErrorOr<BooleanDecoder> initialize(MaybeOwned<BigEndianInputBitStream> bit_stream, size_t size_in_bytes);
+
+    /* (9.2) */
+    static ErrorOr<BooleanDecoder> initialize_vp9(MaybeOwned<BigEndianInputBitStream> bit_stream, size_t size_in_bytes);
+
     ErrorOr<bool> read_bool(u8 probability);
     ErrorOr<u8> read_literal(u8 bits);
-    ErrorOr<void> finish_decode();
+
+    ErrorOr<void> finish_decode_vp9();
 
 private:
     BooleanDecoder(MaybeOwned<BigEndianInputBitStream>&& bit_stream, u8 value, u8 range, u64 bits_left)

Userland/Libraries/LibVideo/VP9/Context.h

@@ -229,7 +229,7 @@ public:
         auto context_view = frame_context.m_block_contexts.view(rows_start, columns_start, height, width);
 
         auto bit_stream = DECODER_TRY_ALLOC(try_make<BigEndianInputBitStream>(DECODER_TRY_ALLOC(try_make<FixedMemoryStream>(*frame_context.stream))));
-        auto decoder = DECODER_TRY(DecoderErrorCategory::Corrupted, BooleanDecoder::initialize(move(bit_stream), tile_size));
+        auto decoder = DECODER_TRY(DecoderErrorCategory::Corrupted, BooleanDecoder::initialize_vp9(move(bit_stream), tile_size));
 
         return TileContext {
             frame_context,

Userland/Libraries/LibVideo/VP9/Parser.cpp

@@ -593,7 +593,7 @@ void Parser::setup_past_independence()
 
 DecoderErrorOr<void> Parser::compressed_header(FrameContext& frame_context)
 {
-    auto decoder = TRY_READ(BooleanDecoder::initialize(MaybeOwned(frame_context.bit_stream), frame_context.header_size_in_bytes));
+    auto decoder = TRY_READ(BooleanDecoder::initialize_vp9(MaybeOwned(frame_context.bit_stream), frame_context.header_size_in_bytes));
     frame_context.transform_mode = TRY(read_tx_mode(decoder, frame_context));
     if (frame_context.transform_mode == TransformMode::Select)
         TRY(tx_mode_probs(decoder));
@@ -610,7 +610,7 @@ DecoderErrorOr<void> Parser::compressed_header(FrameContext& frame_context)
         TRY(read_partition_probs(decoder));
         TRY(mv_probs(decoder, frame_context));
     }
-    TRY_READ(decoder.finish_decode());
+    TRY_READ(decoder.finish_decode_vp9());
     return {};
 }
 
@@ -1002,7 +1002,7 @@ DecoderErrorOr<void> Parser::decode_tile(TileContext& tile_context)
             TRY(decode_partition(tile_context, row, col, Block_64x64));
         }
     }
-    TRY_READ(tile_context.decoder.finish_decode());
+    TRY_READ(tile_context.decoder.finish_decode_vp9());
     return {};
 }