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

mojo/public/cpp/bindings/tests/struct_with_traits_impl.h

Index: mojo/public/cpp/bindings/tests/struct_with_traits_impl.h
diff --git a/mojo/public/cpp/bindings/tests/struct_with_traits_impl.h b/mojo/public/cpp/bindings/tests/struct_with_traits_impl.h
index 3ba8ef6430abf59f925d9450e4d5ff2cc4928ca6..46ba96cc7bf150f582bb00c1a4e06c052d778516 100644
--- a/mojo/public/cpp/bindings/tests/struct_with_traits_impl.h
+++ b/mojo/public/cpp/bindings/tests/struct_with_traits_impl.h
@@ -8,12 +8,22 @@
 #include <stdint.h>
 
 #include <string>
+#include <vector>
 
 #include "base/strings/string_piece.h"
 
 namespace mojo {
 namespace test {
 
+struct StructWithTraitsElementImpl {
+ public:
+  bool operator==(const StructWithTraitsElementImpl& other) const {
+    return value == other.value;
+  }
+
+  int32_t value = 0;
+};
+
 // A type which knows how to look like a mojo::test::StructWithTraits mojom type
 // by way of mojo::StructTraits.
 class StructWithTraitsImpl {
@@ -31,13 +41,32 @@ class StructWithTraitsImpl {
   uint64_t get_uint64() const { return uint64_; }
 
   void set_string(std::string value) { string_ = value; }
-  base::StringPiece get_string() const { return string_; }
+  base::StringPiece get_string_as_string_piece() const { return string_; }
+  const std::string& get_string() const { return string_; }
+
+  const std::vector<std::string>& get_array_string() const {
+    return array_string_;
+  }
+  std::vector<std::string>& get_mutable_array_string() { return array_string_; }
+
+  const StructWithTraitsElementImpl& get_element() const { return element_; }
+  StructWithTraitsElementImpl& get_mutable_element() { return element_; }
+
+  const std::vector<StructWithTraitsElementImpl>& get_array_element() const {
+    return array_element_;
+  }
+  std::vector<StructWithTraitsElementImpl>& get_mutable_array_element() {
+    return array_element_;
+  }
 
  private:
   bool bool_ = false;
   uint32_t uint32_ = 0;
   uint64_t uint64_ = 0;
   std::string string_;
+  std::vector<std::string> array_string_;
+  StructWithTraitsElementImpl element_;
+  std::vector<StructWithTraitsElementImpl> array_element_;
 };
 
 }  // namespace test