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
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@@ 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()) {

[Peter Kasting, 2016/04/12 22:56:25]

Add a comment describing the sequence that can result in this.

[scroggo_chromium, 2016/04/13 12:16:43]

Done.

+        // This data has already been parsed.
+        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;
 }