Avoid undefined behavior when checking for pointer wraparound

base/pickle.cc

Index: base/pickle.cc
===================================================================
--- base/pickle.cc	(revision 232266)
+++ base/pickle.cc	(working copy)
@@ -35,7 +35,7 @@
 template<typename Type>
 inline const char* PickleIterator::GetReadPointerAndAdvance() {
   const char* current_read_ptr = read_ptr_;
-  if (read_ptr_ + sizeof(Type) > read_end_ptr_)
+  if (sizeof(Type) > static_cast<size_t>(read_end_ptr_ - read_ptr_))
     return NULL;
   if (sizeof(Type) < sizeof(uint32))
     read_ptr_ += AlignInt(sizeof(Type), sizeof(uint32));
@@ -291,11 +291,10 @@
 
   const Header* hdr = reinterpret_cast<const Header*>(start);
   const char* payload_base = start + header_size;
-  const char* payload_end = payload_base + hdr->payload_size;
-  if (payload_end < payload_base)
+  if (hdr->payload_size > static_cast<size_t>(end - payload_base))
     return NULL;
 
-  return (payload_end > end) ? NULL : payload_end;
+  return payload_base + hdr->payload_size;
 }
 
 template <size_t length> void Pickle::WriteBytesStatic(const void* data) {