Add helpers for logging mojom objects.

mojo/public/cpp/bindings/tests/map_unittest.cc

Index: mojo/public/cpp/bindings/tests/map_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/map_unittest.cc b/mojo/public/cpp/bindings/tests/map_unittest.cc
index 3df89d305ce9e0f6054eb588374d118993552aec..81375cdeffa9e0e63c3a2f9ab2c9f04429a5cdcf 100644
--- a/mojo/public/cpp/bindings/tests/map_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/map_unittest.cc
@@ -31,10 +31,10 @@ struct StringIntData {
   const char* string_data;
   int int_data;
 } kStringIntData[] = {
-      {"one", 1},
-      {"two", 2},
-      {"three", 3},
-      {"four", 4},
+    {"one", 1},
+    {"two", 2},
+    {"three", 3},
+    {"four", 4},
 };
 
 const size_t kStringIntDataSize = 4;
@@ -433,6 +433,30 @@ TEST_F(MapTest, Serialization_MapOfNullableStructs) {
   EXPECT_EQ(4, map2[1]->height);
 }
 
+TEST_F(MapTest, OutputFormatting) {
+  Map<int32_t, std::string> null_map;
+  Map<int32_t, std::string> empty_map;
+  empty_map.mark_non_null();
+  Map<int32_t, std::string> one_element_map;
+  one_element_map.insert(123, "abc");
+  Map<int32_t, std::string> three_element_map;
+  three_element_map.insert(4, "d");
+  three_element_map.insert(5, "e");
+  three_element_map.insert(6, "f");
+
+  std::ostringstream so;
+  so << "null_map=" << null_map << ", empty_map=" << empty_map
+     << ", one_element_map=" << one_element_map
+     << ", three_element_map=" << three_element_map;
+
+  EXPECT_EQ(
+      "null_map=null, "
+      "empty_map=[], "
+      "one_element_map=[{123: abc}], "
+      "three_element_map=[{4: d}, {5: e}, {6: f}]",
+      so.str());
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace mojo