Add helpers for logging mojom objects.

mojo/public/cpp/bindings/array.h

 // Copyright 2013 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 MOJO_PUBLIC_CPP_BINDINGS_ARRAY_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_ARRAY_H_
 
 #include <string.h>
 
 #include <algorithm>
 #include <cstddef>
+#include <iosfwd>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "mojo/public/cpp/bindings/lib/array_internal.h"
 #include "mojo/public/cpp/bindings/lib/bindings_internal.h"
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 #include "mojo/public/cpp/bindings/type_converter.h"
 
 namespace mojo {
@@ skipping 280 matching lines @@
   static std::set<E> Convert(const Array<T>& input) {
     std::set<E> result;
     if (!input.is_null()) {
       for (size_t i = 0; i < input.size(); ++i)
         result.insert(TypeConverter<E, T>::Convert(input[i]));
     }
     return result;
   }
 };
 
+// Prints the contents of an array to an output stream for debugging purposes.
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const mojo::Array<T>& array) {
+  if (array) {
+    os << "[";
+    bool first = true;
+    for (auto it = array.storage().cbegin(); it != array.storage().cend();
+         ++it) {
+      if (first)
+        first = false;
+      else
+        os << ", ";
+      os << *it;
+    }
+    os << "]";
+  } else {
+    os << "null";
+  }
+  return os;
+}
+
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_ARRAY_H_