Eliminate copies of encoded image data

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

 /* -*- 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,
@@ skipping 369 matching lines @@
 
     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)
 {
-    ASSERT(m_bytesRead <= m_data->size());
+    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) {
@@ skipping 439 matching lines @@
     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;
 }