Mojo C++ bindings: add StringTraits and ArrayTraits for STL types.

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

 // Copyright 2015 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.
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
@@ skipping 196 matching lines @@
     loop.Run();
   }
 }
 
 TEST_F(StructTraitsTest, FieldTypes) {
   StructWithTraitsImpl input;
   input.set_bool(true);
   input.set_uint32(7);
   input.set_uint64(42);
   input.set_string("hello world!");
+  input.get_mutable_array_string().assign({"hello", "world!"});
+  input.get_mutable_element().value = 42;
+  input.get_mutable_array_element().resize(2);
+  input.get_mutable_array_element()[0].value = 1;
+  input.get_mutable_array_element()[1].value = 2;
 
   base::RunLoop loop;
   TraitsTestServicePtr proxy = GetTraitsTestProxy();
   proxy->PassStructWithTraits(
       input,
       [&] (const StructWithTraitsImpl& passed) {
         EXPECT_EQ(input.get_bool(), passed.get_bool());
         EXPECT_EQ(input.get_uint32(), passed.get_uint32());
         EXPECT_EQ(input.get_uint64(), passed.get_uint64());
         EXPECT_EQ(input.get_string(), passed.get_string());
+        EXPECT_EQ(input.get_array_string(), passed.get_array_string());
+        EXPECT_EQ(input.get_element(), passed.get_element());
+        EXPECT_EQ(input.get_array_element(), passed.get_array_element());
         loop.Quit();
       });
   loop.Run();
 }
 
 }  // namespace test
 }  // namespace mojo