Move gif image decoder to SkCodec

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

Index: third_party/WebKit/Source/platform/image-decoders/gif/GIFImageReader.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageReader.cpp b/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageReader.cpp
deleted file mode 100644
index 48aa91cdfd16fb450afec938989bc8384a4d2952..0000000000000000000000000000000000000000
--- a/third_party/WebKit/Source/platform/image-decoders/gif/GIFImageReader.cpp
+++ /dev/null
@@ -1,890 +0,0 @@
-/* -*- Mode: C; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* ***** BEGIN LICENSE BLOCK *****
- * Version: MPL 1.1/GPL 2.0/LGPL 2.1
- *
- * The contents of this file are subject to the Mozilla Public License Version
- * 1.1 (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- * http://www.mozilla.org/MPL/
- *
- * Software distributed under the License is distributed on an "AS IS" basis,
- * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
- * for the specific language governing rights and limitations under the
- * License.
- *
- * The Original Code is mozilla.org code.
- *
- * The Initial Developer of the Original Code is
- * Netscape Communications Corporation.
- * Portions created by the Initial Developer are Copyright (C) 1998
- * the Initial Developer. All Rights Reserved.
- *
- * Contributor(s):
- *   Chris Saari <saari@netscape.com>
- *   Apple Computer
- *
- * Alternatively, the contents of this file may be used under the terms of
- * either the GNU General Public License Version 2 or later (the "GPL"), or
- * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
- * in which case the provisions of the GPL or the LGPL are applicable instead
- * of those above. If you wish to allow use of your version of this file only
- * under the terms of either the GPL or the LGPL, and not to allow others to
- * use your version of this file under the terms of the MPL, indicate your
- * decision by deleting the provisions above and replace them with the notice
- * and other provisions required by the GPL or the LGPL. If you do not delete
- * the provisions above, a recipient may use your version of this file under
- * the terms of any one of the MPL, the GPL or the LGPL.
- *
- * ***** END LICENSE BLOCK ***** */
-
-/*
-The Graphics Interchange Format(c) is the copyright property of CompuServe
-Incorporated. Only CompuServe Incorporated is authorized to define, redefine,
-enhance, alter, modify or change in any way the definition of the format.
-
-CompuServe Incorporated hereby grants a limited, non-exclusive, royalty-free
-license for the use of the Graphics Interchange Format(sm) in computer
-software; computer software utilizing GIF(sm) must acknowledge ownership of the
-Graphics Interchange Format and its Service Mark by CompuServe Incorporated, in
-User and Technical Documentation. Computer software utilizing GIF, which is
-distributed or may be distributed without User or Technical Documentation must
-display to the screen or printer a message acknowledging ownership of the
-Graphics Interchange Format and the Service Mark by CompuServe Incorporated; in
-this case, the acknowledgement may be displayed in an opening screen or leading
-banner, or a closing screen or trailing banner. A message such as the following
-may be used:
-
-    "The Graphics Interchange Format(c) is the Copyright property of
-    CompuServe Incorporated. GIF(sm) is a Service Mark property of
-    CompuServe Incorporated."
-
-For further information, please contact :
-
-    CompuServe Incorporated
-    Graphics Technology Department
-    5000 Arlington Center Boulevard
-    Columbus, Ohio  43220
-    U. S. A.
-
-CompuServe Incorporated maintains a mailing list with all those individuals and
-organizations who wish to receive copies of this document when it is corrected
-or revised. This service is offered free of charge; please provide us with your
-mailing address.
-*/
-
-#include "platform/image-decoders/gif/GIFImageReader.h"
-
-#include <string.h>
-#include "platform/wtf/PtrUtil.h"
-
-using blink::GIFImageDecoder;
-
-// GETN(n, s) requests at least 'n' bytes available from 'q', at start of state
-// 's'.
-//
-// Note: the hold will never need to be bigger than 256 bytes, as each GIF block
-// (except colormaps) can never be bigger than 256 bytes. Colormaps are directly
-// copied in the resp. global_colormap or dynamically allocated local_colormap,
-// so a fixed buffer in GIFImageReader is good enough. This buffer is only
-// needed to copy left-over data from one GifWrite call to the next.
-#define GETN(n, s)          \
-  do {                      \
-    m_bytesToConsume = (n); \
-    m_state = (s);          \
-  } while (0)
-
-// Get a 16-bit value stored in little-endian format.
-#define GETINT16(p) ((p)[1] << 8 | (p)[0])
-
-// Send the data to the display front-end.
-bool GIFLZWContext::outputRow(GIFRow::const_iterator rowBegin) {
-  int drowStart = irow;
-  int drowEnd = irow;
-
-  // Haeberli-inspired hack for interlaced GIFs: Replicate lines while
-  // displaying to diminish the "venetian-blind" effect as the image is
-  // loaded. Adjust pixel vertical positions to avoid the appearance of the
-  // image crawling up the screen as successive passes are drawn.
-  if (m_frameContext->progressiveDisplay() && m_frameContext->interlaced() &&
-      ipass < 4) {
-    unsigned rowDup = 0;
-    unsigned rowShift = 0;
-
-    switch (ipass) {
-      case 1:
-        rowDup = 7;
-        rowShift = 3;
-        break;
-      case 2:
-        rowDup = 3;
-        rowShift = 1;
-        break;
-      case 3:
-        rowDup = 1;
-        rowShift = 0;
-        break;
-      default:
-        break;
-    }
-
-    drowStart -= rowShift;
-    drowEnd = drowStart + rowDup;
-
-    // Extend if bottom edge isn't covered because of the shift upward.
-    if (((m_frameContext->height() - 1) - drowEnd) <= rowShift)
-      drowEnd = m_frameContext->height() - 1;
-
-    // Clamp first and last rows to upper and lower edge of image.
-    if (drowStart < 0)
-      drowStart = 0;
-
-    if ((unsigned)drowEnd >= m_frameContext->height())
-      drowEnd = m_frameContext->height() - 1;
-  }
-
-  // Protect against too much image data.
-  if ((unsigned)drowStart >= m_frameContext->height())
-    return true;
-
-  // CALLBACK: Let the client know we have decoded a row.
-  if (!m_client->HaveDecodedRow(m_frameContext->frameId(), rowBegin,
-                                m_frameContext->width(), drowStart,
-                                drowEnd - drowStart + 1,
-                                m_frameContext->progressiveDisplay() &&
-                                    m_frameContext->interlaced() && ipass > 1))
-    return false;
-
-  if (!m_frameContext->interlaced())
-    irow++;
-  else {
-    do {
-      switch (ipass) {
-        case 1:
-          irow += 8;
-          if (irow >= m_frameContext->height()) {
-            ipass++;
-            irow = 4;
-          }
-          break;
-
-        case 2:
-          irow += 8;
-          if (irow >= m_frameContext->height()) {
-            ipass++;
-            irow = 2;
-          }
-          break;
-
-        case 3:
-          irow += 4;
-          if (irow >= m_frameContext->height()) {
-            ipass++;
-            irow = 1;
-          }
-          break;
-
-        case 4:
-          irow += 2;
-          if (irow >= m_frameContext->height()) {
-            ipass++;
-            irow = 0;
-          }
-          break;
-
-        default:
-          break;
-      }
-    } while (irow > (m_frameContext->height() - 1));
-  }
-  return true;
-}
-
-// Performs Lempel-Ziv-Welch decoding. Returns whether decoding was successful.
-// If successful, the block will have been completely consumed and/or
-// rowsRemaining will be 0.
-bool GIFLZWContext::doLZW(const unsigned char* block, size_t bytesInBlock) {
-  const size_t width = m_frameContext->width();
-
-  if (rowIter == rowBuffer.end())
-    return true;
-
-  for (const unsigned char* ch = block; bytesInBlock-- > 0; ch++) {
-    // Feed the next byte into the decoder's 32-bit input buffer.
-    datum += ((int)*ch) << bits;
-    bits += 8;
-
-    // Check for underflow of decoder's 32-bit input buffer.
-    while (bits >= codesize) {
-      // Get the leading variable-length symbol from the data stream.
-      int code = datum & codemask;
-      datum >>= codesize;
-      bits -= codesize;
-
-      // Reset the dictionary to its original state, if requested.
-      if (code == clearCode) {
-        codesize = m_frameContext->dataSize() + 1;
-        codemask = (1 << codesize) - 1;
-        avail = clearCode + 2;
-        oldcode = -1;
-        continue;
-      }
-
-      // Check for explicit end-of-stream code.
-      if (code == (clearCode + 1)) {
-        // end-of-stream should only appear after all image data.
-        if (!rowsRemaining)
-          return true;
-        return false;
-      }
-
-      const int tempCode = code;
-      unsigned short codeLength = 0;
-      if (code < avail) {
-        // This is a pre-existing code, so we already know what it
-        // encodes.
-        codeLength = suffixLength[code];
-        rowIter += codeLength;
-      } else if (code == avail && oldcode != -1) {
-        // This is a new code just being added to the dictionary.
-        // It must encode the contents of the previous code, plus
-        // the first character of the previous code again.
-        codeLength = suffixLength[oldcode] + 1;
-        rowIter += codeLength;
-        *--rowIter = firstchar;
-        code = oldcode;
-      } else {
-        // This is an invalid code. The dictionary is just initialized
-        // and the code is incomplete. We don't know how to handle
-        // this case.
-        return false;
-      }
-
-      while (code >= clearCode) {
-        *--rowIter = suffix[code];
-        code = prefix[code];
-      }
-
-      *--rowIter = firstchar = suffix[code];
-
-      // Define a new codeword in the dictionary as long as we've read
-      // more than one value from the stream.
-      if (avail < MAX_DICTIONARY_ENTRIES && oldcode != -1) {
-        prefix[avail] = oldcode;
-        suffix[avail] = firstchar;
-        suffixLength[avail] = suffixLength[oldcode] + 1;
-        ++avail;
-
-        // If we've used up all the codewords of a given length
-        // increase the length of codewords by one bit, but don't
-        // exceed the specified maximum codeword size.
-        if (!(avail & codemask) && avail < MAX_DICTIONARY_ENTRIES) {
-          ++codesize;
-          codemask += avail;
-        }
-      }
-      oldcode = tempCode;
-      rowIter += codeLength;
-
-      // Output as many rows as possible.
-      GIFRow::iterator rowBegin = rowBuffer.begin();
-      for (; rowBegin + width <= rowIter; rowBegin += width) {
-        if (!outputRow(rowBegin))
-          return false;
-        rowsRemaining--;
-        if (!rowsRemaining)
-          return true;
-      }
-
-      if (rowBegin != rowBuffer.begin()) {
-        // Move the remaining bytes to the beginning of the buffer.
-        const size_t bytesToCopy = rowIter - rowBegin;
-        memcpy(rowBuffer.begin(), rowBegin, bytesToCopy);
-        rowIter = rowBuffer.begin() + bytesToCopy;
-      }
-    }
-  }
-  return true;
-}
-
-void GIFColorMap::buildTable(blink::FastSharedBufferReader* reader) {
-  if (!m_isDefined || !m_table.IsEmpty())
-    return;
-
-  RELEASE_ASSERT(m_position + m_colors * BYTES_PER_COLORMAP_ENTRY <=
-                 reader->size());
-  DCHECK_LE(m_colors, MAX_COLORS);
-  char buffer[MAX_COLORS * BYTES_PER_COLORMAP_ENTRY];
-  const unsigned char* srcColormap =
-      reinterpret_cast<const unsigned char*>(reader->GetConsecutiveData(
-          m_position, m_colors * BYTES_PER_COLORMAP_ENTRY, buffer));
-  m_table.Resize(m_colors);
-  for (Table::iterator iter = m_table.begin(); iter != m_table.end(); ++iter) {
-    *iter = SkPackARGB32NoCheck(255, srcColormap[0], srcColormap[1],
-                                srcColormap[2]);
-    srcColormap += BYTES_PER_COLORMAP_ENTRY;
-  }
-}
-
-// Decodes this frame. |frameDecoded| will be set to true if the entire frame is
-// decoded. Returns true if decoding progressed further than before without
-// error, or there is insufficient new data to decode further. Otherwise, a
-// decoding error occurred; returns false in this case.
-bool GIFFrameContext::decode(blink::FastSharedBufferReader* reader,
-                             blink::GIFImageDecoder* client,
-                             bool* frameDecoded) {
-  m_localColorMap.buildTable(reader);
-
-  *frameDecoded = false;
-  if (!m_lzwContext) {
-    // Wait for more data to properly initialize GIFLZWContext.
-    if (!isDataSizeDefined() || !isHeaderDefined())
-      return true;
-
-    m_lzwContext = WTF::MakeUnique<GIFLZWContext>(client, this);
-    if (!m_lzwContext->prepareToDecode()) {
-      m_lzwContext.reset();
-      return false;
-    }
-
-    m_currentLzwBlock = 0;
-  }
-
-  // Some bad GIFs have extra blocks beyond the last row, which we don't want to
-  // decode.
-  while (m_currentLzwBlock < m_lzwBlocks.size() &&
-         m_lzwContext->hasRemainingRows()) {
-    size_t blockPosition = m_lzwBlocks[m_currentLzwBlock].blockPosition;
-    size_t blockSize = m_lzwBlocks[m_currentLzwBlock].blockSize;
-    if (blockPosition + blockSize > reader->size())
-      return false;
-
-    while (blockSize) {
-      const char* segment = 0;
-      size_t segmentLength = reader->GetSomeData(segment, blockPosition);
-      size_t decodeSize = std::min(segmentLength, blockSize);
-      if (!m_lzwContext->doLZW(reinterpret_cast<const unsigned char*>(segment),
-                               decodeSize))
-        return false;
-      blockPosition += decodeSize;
-      blockSize -= decodeSize;
-    }
-    ++m_currentLzwBlock;
-  }
-
-  // If this frame is data complete then the previous loop must have completely
-  // decoded all LZW blocks.
-  // There will be no more decoding for this frame so it's time to cleanup.
-  if (isComplete()) {
-    *frameDecoded = true;
-    m_lzwContext.reset();
-  }
-  return true;
-}
-
-// Decodes a frame using GIFFrameContext:decode(). Returns true if decoding has
-// progressed, or false if an error has occurred.
-bool GIFImageReader::decode(size_t frameIndex) {
-  blink::FastSharedBufferReader reader(m_data);
-  m_globalColorMap.buildTable(&reader);
-
-  bool frameDecoded = false;
-  GIFFrameContext* currentFrame = m_frames[frameIndex].get();
-
-  return currentFrame->decode(&reader, m_client, &frameDecoded) &&
-         (!frameDecoded || m_client->FrameComplete(frameIndex));
-}
-
-bool GIFImageReader::parse(GIFImageDecoder::GIFParseQuery query) {
-  if (m_bytesRead >= m_data->size()) {
-    // This data has already been parsed. For example, in deferred
-    // decoding, a DecodingImageGenerator with more data may have already
-    // used this same ImageDecoder to decode. This can happen if two
-    // SkImages created by a DeferredImageDecoder are drawn/prerolled
-    // out of order (with respect to how much data they had at creation
-    // time).
-    return !m_client->Failed();
-  }
-
-  return parseData(m_bytesRead, m_data->size() - m_bytesRead, query);
-}
-
-// Parse incoming GIF data stream into internal data structures.
-// Return true if parsing has progressed or there is not enough data.
-// Return false if a fatal error is encountered.
-bool GIFImageReader::parseData(size_t dataPosition,
-                               size_t len,
-                               GIFImageDecoder::GIFParseQuery query) {
-  if (!len) {
-    // No new data has come in since the last call, just ignore this call.
-    return true;
-  }
-
-  if (len < m_bytesToConsume)
-    return true;
-
-  blink::FastSharedBufferReader reader(m_data);
-
-  // A read buffer of 16 bytes is enough to accomodate all possible reads for
-  // parsing.
-  char readBuffer[16];
-
-  // Read as many components from |m_data| as possible. At the beginning of each
-  // iteration, |dataPosition| is advanced by m_bytesToConsume to point to the
-  // next component. |len| is decremented accordingly.
-  while (len >= m_bytesToConsume) {
-    const size_t currentComponentPosition = dataPosition;
-
-    // Mark the current component as consumed. Note that currentComponent will
-    // remain pointed at this component until the next loop iteration.
-    dataPosition += m_bytesToConsume;
-    len -= m_bytesToConsume;
-
-    switch (m_state) {
-      case GIFLZW:
-        DCHECK(!m_frames.IsEmpty());
-        // m_bytesToConsume is the current component size because it hasn't been
-        // updated.
-        m_frames.back()->addLzwBlock(currentComponentPosition,
-                                     m_bytesToConsume);
-        GETN(1, GIFSubBlock);
-        break;
-
-      case GIFLZWStart: {
-        DCHECK(!m_frames.IsEmpty());
-        m_frames.back()->setDataSize(static_cast<unsigned char>(
-            reader.GetOneByte(currentComponentPosition)));
-        GETN(1, GIFSubBlock);
-        break;
-      }
-
-      case GIFType: {
-        const char* currentComponent =
-            reader.GetConsecutiveData(currentComponentPosition, 6, readBuffer);
-
-        // All GIF files begin with "GIF87a" or "GIF89a".
-        if (!memcmp(currentComponent, "GIF89a", 6))
-          m_version = 89;
-        else if (!memcmp(currentComponent, "GIF87a", 6))
-          m_version = 87;
-        else
-          return false;
-        GETN(7, GIFGlobalHeader);
-        break;
-      }
-
-      case GIFGlobalHeader: {
-        const unsigned char* currentComponent =
-            reinterpret_cast<const unsigned char*>(reader.GetConsecutiveData(
-                currentComponentPosition, 5, readBuffer));
-
-        // This is the height and width of the "screen" or frame into which
-        // images are rendered. The individual images can be smaller than
-        // the screen size and located with an origin anywhere within the
-        // screen.
-        // Note that we don't inform the client of the size yet, as it might
-        // change after we read the first frame's image header.
-        m_screenWidth = GETINT16(currentComponent);
-        m_screenHeight = GETINT16(currentComponent + 2);
-
-        const size_t globalColorMapColors = 2 << (currentComponent[4] & 0x07);
-
-        if ((currentComponent[4] & 0x80) &&
-            globalColorMapColors > 0) { /* global map */
-          m_globalColorMap.setTablePositionAndSize(dataPosition,
-                                                   globalColorMapColors);
-          GETN(BYTES_PER_COLORMAP_ENTRY * globalColorMapColors,
-               GIFGlobalColormap);
-          break;
-        }
-
-        GETN(1, GIFImageStart);
-        break;
-      }
-
-      case GIFGlobalColormap: {
-        m_globalColorMap.setDefined();
-        GETN(1, GIFImageStart);
-        break;
-      }
-
-      case GIFImageStart: {
-        const char currentComponent =
-            reader.GetOneByte(currentComponentPosition);
-
-        if (currentComponent == '!') {  // extension.
-          GETN(2, GIFExtension);
-          break;
-        }
-
-        if (currentComponent == ',') {  // image separator.
-          GETN(9, GIFImageHeader);
-          break;
-        }
-
-        // If we get anything other than ',' (image separator), '!'
-        // (extension), or ';' (trailer), there is extraneous data
-        // between blocks. The GIF87a spec tells us to keep reading
-        // until we find an image separator, but GIF89a says such
-        // a file is corrupt. We follow Mozilla's implementation and
-        // proceed as if the file were correctly terminated, so the
-        // GIF will display.
-        GETN(0, GIFDone);
-        break;
-      }
-
-      case GIFExtension: {
-        const unsigned char* currentComponent =
-            reinterpret_cast<const unsigned char*>(reader.GetConsecutiveData(
-                currentComponentPosition, 2, readBuffer));
-
-        size_t bytesInBlock = currentComponent[1];
-        GIFState exceptionState = GIFSkipBlock;
-
-        switch (*currentComponent) {
-          case 0xf9:
-            exceptionState = GIFControlExtension;
-            // The GIF spec mandates that the GIFControlExtension header block
-            // length is 4 bytes, and the parser for this block reads 4 bytes,
-            // so we must enforce that the buffer contains at least this many
-            // bytes. If the GIF specifies a different length, we allow that, so
-            // long as it's larger; the additional data will simply be ignored.
-            bytesInBlock = std::max(bytesInBlock, static_cast<size_t>(4));
-            break;
-
-          // The GIF spec also specifies the lengths of the following two
-          // extensions' headers (as 12 and 11 bytes, respectively). Because we
-          // ignore the plain text extension entirely and sanity-check the
-          // actual length of the application extension header before reading
-          // it, we allow GIFs to deviate from these values in either direction.
-          // This is important for real-world compatibility, as GIFs in the wild
-          // exist with application extension headers that are both shorter and
-          // longer than 11 bytes.
-          case 0x01:
-            // ignoring plain text extension
-            break;
-
-          case 0xff:
-            exceptionState = GIFApplicationExtension;
-            break;
-
-          case 0xfe:
-            exceptionState = GIFConsumeComment;
-            break;
-        }
-
-        if (bytesInBlock)
-          GETN(bytesInBlock, exceptionState);
-        else
-          GETN(1, GIFImageStart);
-        break;
-      }
-
-      case GIFConsumeBlock: {
-        const unsigned char currentComponent = static_cast<unsigned char>(
-            reader.GetOneByte(currentComponentPosition));
-        if (!currentComponent)
-          GETN(1, GIFImageStart);
-        else
-          GETN(currentComponent, GIFSkipBlock);
-        break;
-      }
-
-      case GIFSkipBlock: {
-        GETN(1, GIFConsumeBlock);
-        break;
-      }
-
-      case GIFControlExtension: {
-        const unsigned char* currentComponent =
-            reinterpret_cast<const unsigned char*>(reader.GetConsecutiveData(
-                currentComponentPosition, 4, readBuffer));
-
-        addFrameIfNecessary();
-        GIFFrameContext* currentFrame = m_frames.back().get();
-        if (*currentComponent & 0x1)
-          currentFrame->setTransparentPixel(currentComponent[3]);
-
-        // We ignore the "user input" bit.
-
-        // NOTE: This relies on the values in the FrameDisposalMethod enum
-        // matching those in the GIF spec!
-        int disposalMethod = ((*currentComponent) >> 2) & 0x7;
-        if (disposalMethod < 4) {
-          currentFrame->setDisposalMethod(
-              static_cast<blink::ImageFrame::DisposalMethod>(disposalMethod));
-        } else if (disposalMethod == 4) {
-          // Some specs say that disposal method 3 is "overwrite previous",
-          // others that setting the third bit of the field (i.e. method 4) is.
-          // We map both to the same value.
-          currentFrame->setDisposalMethod(
-              blink::ImageFrame::kDisposeOverwritePrevious);
-        }
-        currentFrame->setDelayTime(GETINT16(currentComponent + 1) * 10);
-        GETN(1, GIFConsumeBlock);
-        break;
-      }
-
-      case GIFCommentExtension: {
-        const unsigned char currentComponent = static_cast<unsigned char>(
-            reader.GetOneByte(currentComponentPosition));
-        if (currentComponent)
-          GETN(currentComponent, GIFConsumeComment);
-        else
-          GETN(1, GIFImageStart);
-        break;
-      }
-
-      case GIFConsumeComment: {
-        GETN(1, GIFCommentExtension);
-        break;
-      }
-
-      case GIFApplicationExtension: {
-        // Check for netscape application extension.
-        if (m_bytesToConsume == 11) {
-          const unsigned char* currentComponent =
-              reinterpret_cast<const unsigned char*>(reader.GetConsecutiveData(
-                  currentComponentPosition, 11, readBuffer));
-
-          if (!memcmp(currentComponent, "NETSCAPE2.0", 11) ||
-              !memcmp(currentComponent, "ANIMEXTS1.0", 11))
-            GETN(1, GIFNetscapeExtensionBlock);
-        }
-
-        if (m_state != GIFNetscapeExtensionBlock)
-          GETN(1, GIFConsumeBlock);
-        break;
-      }
-
-      // Netscape-specific GIF extension: animation looping.
-      case GIFNetscapeExtensionBlock: {
-        const int currentComponent = static_cast<unsigned char>(
-            reader.GetOneByte(currentComponentPosition));
-        // GIFConsumeNetscapeExtension always reads 3 bytes from the stream; we
-        // should at least wait for this amount.
-        if (currentComponent)
-          GETN(std::max(3, currentComponent), GIFConsumeNetscapeExtension);
-        else
-          GETN(1, GIFImageStart);
-        break;
-      }
-
-      // Parse netscape-specific application extensions
-      case GIFConsumeNetscapeExtension: {
-        const unsigned char* currentComponent =
-            reinterpret_cast<const unsigned char*>(reader.GetConsecutiveData(
-                currentComponentPosition, 3, readBuffer));
-
-        int netscapeExtension = currentComponent[0] & 7;
-
-        // Loop entire animation specified # of times. Only read the loop count
-        // during the first iteration.
-        if (netscapeExtension == 1) {
-          m_loopCount = GETINT16(currentComponent + 1);
-
-          // Zero loop count is infinite animation loop request.
-          if (!m_loopCount)
-            m_loopCount = blink::kCAnimationLoopInfinite;
-
-          GETN(1, GIFNetscapeExtensionBlock);
-        } else if (netscapeExtension == 2) {
-          // Wait for specified # of bytes to enter buffer.
-
-          // Don't do this, this extension doesn't exist (isn't used at all)
-          // and doesn't do anything, as our streaming/buffering takes care of
-          // it all. See http://semmix.pl/color/exgraf/eeg24.htm .
-          GETN(1, GIFNetscapeExtensionBlock);
-        } else {
-          // 0,3-7 are yet to be defined netscape extension codes
-          return false;
-        }
-        break;
-      }
-
-      case GIFImageHeader: {
-        unsigned height, width, xOffset, yOffset;
-        const unsigned char* currentComponent =
-            reinterpret_cast<const unsigned char*>(reader.GetConsecutiveData(
-                currentComponentPosition, 9, readBuffer));
-
-        /* Get image offsets, with respect to the screen origin */
-        xOffset = GETINT16(currentComponent);
-        yOffset = GETINT16(currentComponent + 2);
-
-        /* Get image width and height. */
-        width = GETINT16(currentComponent + 4);
-        height = GETINT16(currentComponent + 6);
-
-        // Some GIF files have frames that don't fit in the specified
-        // overall image size. For the first frame, we can simply enlarge
-        // the image size to allow the frame to be visible.  We can't do
-        // this on subsequent frames because the rest of the decoding
-        // infrastructure assumes the image size won't change as we
-        // continue decoding, so any subsequent frames that are even
-        // larger will be cropped.
-        // Luckily, handling just the first frame is sufficient to deal
-        // with most cases, e.g. ones where the image size is erroneously
-        // set to zero, since usually the first frame completely fills
-        // the image.
-        if (currentFrameIsFirstFrame()) {
-          m_screenHeight = std::max(m_screenHeight, yOffset + height);
-          m_screenWidth = std::max(m_screenWidth, xOffset + width);
-        }
-
-        // Inform the client of the final size.
-        if (!m_sentSizeToClient && m_client &&
-            !m_client->SetSize(m_screenWidth, m_screenHeight))
-          return false;
-        m_sentSizeToClient = true;
-
-        if (query == GIFImageDecoder::kGIFSizeQuery) {
-          // The decoder needs to stop. Hand back the number of bytes we
-          // consumed from the buffer minus 9 (the amount we consumed to read
-          // the header).
-          setRemainingBytes(len + 9);
-          GETN(9, GIFImageHeader);
-          return true;
-        }
-
-        addFrameIfNecessary();
-        GIFFrameContext* currentFrame = m_frames.back().get();
-
-        currentFrame->setHeaderDefined();
-
-        // Work around more broken GIF files that have zero image width or
-        // height.
-        if (!height || !width) {
-          height = m_screenHeight;
-          width = m_screenWidth;
-          if (!height || !width)
-            return false;
-        }
-        currentFrame->setRect(xOffset, yOffset, width, height);
-        currentFrame->setInterlaced(currentComponent[8] & 0x40);
-
-        // Overlaying interlaced, transparent GIFs over
-        // existing image data using the Haeberli display hack
-        // requires saving the underlying image in order to
-        // avoid jaggies at the transparency edges. We are
-        // unprepared to deal with that, so don't display such
-        // images progressively. Which means only the first
-        // frame can be progressively displayed.
-        // FIXME: It is possible that a non-transparent frame
-        // can be interlaced and progressively displayed.
-        currentFrame->setProgressiveDisplay(currentFrameIsFirstFrame());
-
-        const bool isLocalColormapDefined = currentComponent[8] & 0x80;
-        if (isLocalColormapDefined) {
-          // The three low-order bits of currentComponent[8] specify the bits
-          // per pixel.
-          const size_t numColors = 2 << (currentComponent[8] & 0x7);
-          currentFrame->localColorMap().setTablePositionAndSize(dataPosition,
-                                                                numColors);
-          GETN(BYTES_PER_COLORMAP_ENTRY * numColors, GIFImageColormap);
-          break;
-        }
-
-        GETN(1, GIFLZWStart);
-        break;
-      }
-
-      case GIFImageColormap: {
-        DCHECK(!m_frames.IsEmpty());
-        m_frames.back()->localColorMap().setDefined();
-        GETN(1, GIFLZWStart);
-        break;
-      }
-
-      case GIFSubBlock: {
-        const size_t bytesInBlock = static_cast<unsigned char>(
-            reader.GetOneByte(currentComponentPosition));
-        if (bytesInBlock)
-          GETN(bytesInBlock, GIFLZW);
-        else {
-          // Finished parsing one frame; Process next frame.
-          DCHECK(!m_frames.IsEmpty());
-          // Note that some broken GIF files do not have enough LZW blocks to
-          // fully decode all rows; we treat this case as "frame complete".
-          m_frames.back()->setComplete();
-          GETN(1, GIFImageStart);
-        }
-        break;
-      }
-
-      case GIFDone: {
-        m_parseCompleted = true;
-        return true;
-      }
-
-      default:
-        // We shouldn't ever get here.
-        return false;
-        break;
-    }
-  }
-
-  setRemainingBytes(len);
-  return true;
-}
-
-void GIFImageReader::setRemainingBytes(size_t remainingBytes) {
-  DCHECK_LE(remainingBytes, m_data->size());
-  m_bytesRead = m_data->size() - remainingBytes;
-}
-
-void GIFImageReader::addFrameIfNecessary() {
-  if (m_frames.IsEmpty() || m_frames.back()->isComplete())
-    m_frames.push_back(WTF::WrapUnique(new GIFFrameContext(m_frames.size())));
-}
-
-// FIXME: Move this method to close to doLZW().
-bool GIFLZWContext::prepareToDecode() {
-  DCHECK(m_frameContext->isDataSizeDefined());
-  DCHECK(m_frameContext->isHeaderDefined());
-
-  // Since we use a codesize of 1 more than the datasize, we need to ensure
-  // that our datasize is strictly less than the MAX_DICTIONARY_ENTRY_BITS.
-  if (m_frameContext->dataSize() >= MAX_DICTIONARY_ENTRY_BITS)
-    return false;
-  clearCode = 1 << m_frameContext->dataSize();
-  avail = clearCode + 2;
-  oldcode = -1;
-  codesize = m_frameContext->dataSize() + 1;
-  codemask = (1 << codesize) - 1;
-  datum = bits = 0;
-  ipass = m_frameContext->interlaced() ? 1 : 0;
-  irow = 0;
-
-  // We want to know the longest sequence encodable by a dictionary with
-  // MAX_DICTIONARY_ENTRIES entries. If we ignore the need to encode the base
-  // values themselves at the beginning of the dictionary, as well as the need
-  // for a clear code or a termination code, we could use every entry to
-  // encode a series of multiple values. If the input value stream looked
-  // like "AAAAA..." (a long string of just one value), the first dictionary
-  // entry would encode AA, the next AAA, the next AAAA, and so forth. Thus
-  // the longest sequence would be MAX_DICTIONARY_ENTRIES + 1 values.
-  //
-  // However, we have to account for reserved entries. The first |datasize|
-  // bits are reserved for the base values, and the next two entries are
-  // reserved for the clear code and termination code. In theory a GIF can
-  // set the datasize to 0, meaning we have just two reserved entries, making
-  // the longest sequence (MAX_DICTIONARY_ENTIRES + 1) - 2 values long. Since
-  // each value is a byte, this is also the number of bytes in the longest
-  // encodable sequence.
-  const size_t maxBytes = MAX_DICTIONARY_ENTRIES - 1;
-
-  // Now allocate the output buffer. We decode directly into this buffer
-  // until we have at least one row worth of data, then call outputRow().
-  // This means worst case we may have (row width - 1) bytes in the buffer
-  // and then decode a sequence |maxBytes| long to append.
-  rowBuffer.Resize(m_frameContext->width() - 1 + maxBytes);
-  rowIter = rowBuffer.begin();
-  rowsRemaining = m_frameContext->height();
-
-  // Clearing the whole suffix table lets us be more tolerant of bad data.
-  for (int i = 0; i < clearCode; ++i) {
-    suffix[i] = i;
-    suffixLength[i] = 1;
-  }
-  return true;
-}