[Mac] Convert a DCHECK to a condition in safe_browsing::dmg::UDIFBlockChunkReadStream::Seek.

chrome/utility/safe_browsing/mac/udif.cc

 // Copyright 2015 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.
 
 #include "chrome/utility/safe_browsing/mac/udif.h"
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <bzlib.h>
 #include <libkern/OSByteOrder.h>
 #include <uuid/uuid.h>
@@ skipping 636 matching lines @@
   if (!decompress_read_offset.IsValid()) {
     DLOG(ERROR) << "Partition decompress read offset overflows";
     return -1;
   }
 
   if (!chunk_stream_ || chunk != chunk_stream_->chunk()) {
     chunk_stream_.reset(
         new UDIFBlockChunkReadStream(stream_, block_size_, chunk));
   }
   current_chunk_ = chunk_number;
-  chunk_stream_->Seek(decompress_read_offset.ValueOrDie(), SEEK_SET);
+  if (chunk_stream_->Seek(decompress_read_offset.ValueOrDie(), SEEK_SET) == -1)
+    return -1;
 
   return offset;
 }
 
 UDIFBlockChunkReadStream::UDIFBlockChunkReadStream(ReadStream* stream,
                                                    uint16_t block_size,
                                                    const UDIFBlockChunk* chunk)
     : stream_(stream),
       chunk_(chunk),
       length_in_bytes_(chunk->sector_count * block_size),
@@ skipping 27 matching lines @@
       break;
     case UDIFBlockChunk::Type::LAST_BLOCK:
       *bytes_read = 0;
       return true;
   }
   return false;
 }
 
 off_t UDIFBlockChunkReadStream::Seek(off_t offset, int whence) {
   DCHECK_EQ(SEEK_SET, whence);
-  DCHECK_LT(static_cast<uint64_t>(offset), length_in_bytes_);
+  if (static_cast<uint64_t>(offset) >= length_in_bytes_)
+    return -1;
   offset_ = offset;
   return offset_;
 }
 
 bool UDIFBlockChunkReadStream::CopyOutZeros(uint8_t* buffer,
                                             size_t buffer_size,
                                             size_t* bytes_read) {
   *bytes_read = std::min(buffer_size, length_in_bytes_ - offset_);
   bzero(buffer, *bytes_read);
   offset_ += *bytes_read;
@@ skipping 118 matching lines @@
                 << chunk_->compressed_offset;
     return false;
   }
   return true;
 }
 
 }  // namespace
 
 }  // namespace dmg
 }  // namespace safe_browsing