Eliminate box reordering in media::mp4::BoxReader.

media/mp4/box_reader.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_MP4_BOX_READER_H_
 #define MEDIA_MP4_BOX_READER_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 100 matching lines @@
   // Read at least one child. False means error or no such child present.
   template<typename T> bool ReadChildren(
       std::vector<T>* children) WARN_UNUSED_RESULT;
 
   // Read any number of children. False means error.
   template<typename T> bool MaybeReadChildren(
       std::vector<T>* children) WARN_UNUSED_RESULT;
 
   // Read all children, regardless of FourCC. This is used from exactly one box,
   // corresponding to a rather significant inconsistency in the BMFF spec.
+  // Note that this method is mutually exclusive with ScanChildren().
   template<typename T> bool ReadAllChildren(
       std::vector<T>* children) WARN_UNUSED_RESULT;
 
   // Populate the values of 'version()' and 'flags()' from a full box header.
   // Many boxes, but not all, use these values. This call should happen after
   // the box has been initialized, and does not re-read the main box header.
   bool ReadFullBoxHeader() WARN_UNUSED_RESULT;
 
   FourCC type() const   { return type_; }
   uint8 version() const { return version_; }
@@ skipping 47 matching lines @@
   }
   children_.erase(start_itr, end_itr);
 
   DVLOG(2) << "Found " << children->size() << " "
            << FourCCToString(child_type) << " boxes.";
   return true;
 }
 
 template<typename T>
 bool BoxReader::ReadAllChildren(std::vector<T>* children) {
-  DCHECK(scanned_);
-  DCHECK(children->empty());
-  RCHECK(!children_.empty());
+  DCHECK(!scanned_);
+  scanned_ = true;
 
-  children->resize(children_.size());
-  typename std::vector<T>::iterator child_itr = children->begin();
-  for (ChildMap::iterator itr = children_.begin();
-       itr != children_.end(); ++itr) {
-    RCHECK(child_itr->Parse(&itr->second));
-    ++child_itr;
+  bool err = false;
+  while (pos() < size()) {
+    BoxReader child_reader(&buf_[pos_], size_ - pos_);
+    if (!child_reader.ReadHeader(&err)) break;
+    T child;
+    RCHECK(child.Parse(&child_reader));
+    children->push_back(child);
+    pos_ += child_reader.size();
   }
-  children_.clear();
-  return true;
+
+  return !err;
 }
 
 }  // namespace mp4
 }  // namespace media
 
 #endif  // MEDIA_MP4_BOX_READER_H_