Treat a GIF with no color table as transparent

third_party/gif/SkGifImageReader.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 719 matching lines @@
                 }
             }
 
             const bool isLocalColormapDefined = SkToBool(currentComponent[8] & 0x80);
             // The three low-order bits of currentComponent[8] specify the bits per pixel.
             const size_t numColors = 2 << (currentComponent[8] & 0x7);
             if (currentFrameIsFirstFrame()) {
                 bool hasTransparentPixel;
                 if (m_frames.size() == 0) {
                     // We did not see a Graphics Control Extension, so no transparent
-                    // pixel was specified.
-                    hasTransparentPixel = false;
+                    // pixel was specified. But if there is no color table, this frame is
+                    // still transparent.
+                    hasTransparentPixel = !isLocalColormapDefined
+                                          && m_globalColorMap.numColors() == 0;
                 } else {
                     // This means we did see a Graphics Control Extension, which specifies
                     // the transparent pixel
                     const size_t transparentPixel = m_frames[0]->transparentPixel();
                     if (isLocalColormapDefined) {
                         hasTransparentPixel = transparentPixel < numColors;
                     } else {
                         const size_t globalColors = m_globalColorMap.numColors();
                         if (!globalColors) {
                             // No color table for this frame, so the frame is empty.
@@ skipping 211 matching lines @@
     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;
 }