mojom: Add associative arrays to the mojom language.

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

Index: mojo/public/cpp/bindings/tests/string_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/string_unittest.cc b/mojo/public/cpp/bindings/tests/string_unittest.cc
index 6f8544363ad49886d4981ec1d1443470816ab562..7e3d91024bd2f1f49c10b1001a94d39845693a00 100644
--- a/mojo/public/cpp/bindings/tests/string_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/string_unittest.cc
@@ -61,5 +61,16 @@ TEST(StringTest, Equality) {
   EXPECT_TRUE(s != "not");
 }
 
+TEST(StringTest, LessThanNullness) {
+  String null;
+  String null2;
+  EXPECT_FALSE(null < null2);
+  EXPECT_FALSE(null2 < null);
+
+  String real("real");
+  EXPECT_TRUE(null < real);
+  EXPECT_FALSE(real < null);
+}
+
 }  // namespace test
 }  // namespace mojo