More clear comment for ValidateStructHeader.

mojo/public/cpp/bindings/lib/bindings_serialization.cc

Index: mojo/public/cpp/bindings/lib/bindings_serialization.cc
diff --git a/mojo/public/cpp/bindings/lib/bindings_serialization.cc b/mojo/public/cpp/bindings/lib/bindings_serialization.cc
index d341b21446cd5154caf7a3813988c5091540be99..d5f778536847173015d3326b625750bacf72e29b 100644
--- a/mojo/public/cpp/bindings/lib/bindings_serialization.cc
+++ b/mojo/public/cpp/bindings/lib/bindings_serialization.cc
@@ -84,6 +84,8 @@ bool ValidateStructHeader(const void* data,
                           uint32_t min_num_bytes,
                           uint32_t min_num_fields,
                           BoundsChecker* bounds_checker) {
+  assert(min_num_bytes >= sizeof(StructHeader));
+
   if (!IsAligned(data)) {
     ReportValidationError(VALIDATION_ERROR_MISALIGNED_OBJECT);
     return false;