libwebp: cherry-pick some demux changes

third_party/libwebp/demux/demux.c

Index: third_party/libwebp/demux/demux.c
diff --git a/third_party/libwebp/demux/demux.c b/third_party/libwebp/demux/demux.c
index 9966399f90dbce08dbaa93b2d08e2a70d0e1cc11..c6e4acdcb866c1984a8accf6329f357ce6eed556 100644
--- a/third_party/libwebp/demux/demux.c
+++ b/third_party/libwebp/demux/demux.c
@@ -509,8 +509,9 @@ static ParseStatus ParseVP8X(WebPDemuxer* const dmux) {
       case MKFOURCC('A', 'L', 'P', 'H'):
       case MKFOURCC('V', 'P', '8', ' '):
       case MKFOURCC('V', 'P', '8', 'L'): {
+        const int has_frames = !!(dmux->feature_flags_ & ANIMATION_FLAG);

[fbarchard, 2013/11/23 01:01:57]

!! is obscure.  
const int has_frames = dmux->feature_flags_ & ANIMATION_FLAG;
will do, as long as you use boolean operators.  e.g. || has_frames.
or more conventional would be

(dmux->feature_flags_ & ANIMATION_FLAG) != 0;
or
(dmux->feature_flags_ & ANIMATION_FLAG) == ANIMATION_FLAG;

         // check that this isn't an animation (all frames should be in an ANMF).
-        if (anim_chunks > 0) return PARSE_ERROR;
+        if (anim_chunks > 0 || has_frames) return PARSE_ERROR;
 
         Rewind(mem, CHUNK_HEADER_SIZE);
         status = ParseSingleImage(dmux);
@@ -599,6 +600,8 @@ static int IsValidSimpleFormat(const WebPDemuxer* const dmux) {
 
 // If 'exact' is true, check that the image resolution matches the canvas.
 // If 'exact' is false, check that the x/y offsets do not exceed the canvas.
+// TODO(jzern): this is insufficient in the fragmented image case if the

[fbarchard, 2013/11/23 01:01:57]

Prefer comments start with uppercase.
This is insufficient.
Prefer a todo that indicates the action to be taken, not the problem.
A problem is best documented with a bug #.

+// expectation is that the fragments completely cover the canvas.
 static int CheckFrameBounds(const Frame* const frame, int exact,
                             int canvas_width, int canvas_height) {
   if (exact) {
@@ -626,6 +629,9 @@ static int IsValidExtendedFormat(const WebPDemuxer* const dmux) {
   if (dmux->canvas_width_ <= 0 || dmux->canvas_height_ <= 0) return 0;
   if (dmux->loop_count_ < 0) return 0;
   if (dmux->state_ == WEBP_DEMUX_DONE && dmux->frames_ == NULL) return 0;
+#ifndef WEBP_EXPERIMENTAL_FEATURES
+  if (has_fragments) return 0;
+#endif
 
   while (f != NULL) {
     const int cur_frame_set = f->frame_num_;
@@ -637,8 +643,10 @@ static int IsValidExtendedFormat(const WebPDemuxer* const dmux) {
       const ChunkData* const image = f->img_components_;
       const ChunkData* const alpha = f->img_components_ + 1;
 
+      if (has_fragments && !f->is_fragment_) return 0;
       if (!has_fragments && f->is_fragment_) return 0;
       if (!has_frames && f->frame_num_ > 1) return 0;
+
       if (f->complete_) {
         if (alpha->size_ == 0 && image->size_ == 0) return 0;
         // Ensure alpha precedes image bitstream.