Mojo C++ bindings: better log message for serialization warnings.

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

Index: mojo/public/cpp/bindings/lib/array_internal.cc
diff --git a/mojo/public/cpp/bindings/lib/array_internal.cc b/mojo/public/cpp/bindings/lib/array_internal.cc
index 835b78a5b9a479cfd84afd37bce299b5c071f23d..9f62aa2b20ce5fc4458a29a60bb1baaea8552bab 100644
--- a/mojo/public/cpp/bindings/lib/array_internal.cc
+++ b/mojo/public/cpp/bindings/lib/array_internal.cc
@@ -4,9 +4,28 @@
 
 #include "mojo/public/cpp/bindings/lib/array_internal.h"
 
+#include <sstream>
+
 namespace mojo {
 namespace internal {
 
+std::string MakeMessageWithArrayIndex(const char* message,
+                                      size_t size,
+                                      size_t index) {
+  std::ostringstream stream;
+  stream << message << ": array size - " << size << "; index - " << index;
+  return stream.str();
+}
+
+std::string MakeMessageWithExpectedArraySize(const char* message,
+                                             size_t size,
+                                             size_t expected_size) {
+  std::ostringstream stream;
+  stream << message << ": array size - " << size << "; expected size - "
+         << expected_size;
+  return stream.str();
+}
+
 ArrayDataTraits<bool>::BitRef::~BitRef() {
 }