Mojo C++ bindings: switch the existing usage of StructTraits to use the new data view interface.

mojo/public/cpp/bindings/lib/serialization_util.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_LIB_SERIALIZATION_UTIL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 84 matching lines @@
 
 template <typename T>
 inline void InterfaceDataToPointer(Interface_Data* input,
                                    InterfacePtr<T>* output,
                                    SerializationContext* context) {
   output->Bind(InterfacePtrInfo<T>(
       context->handles.TakeHandleAs<mojo::MessagePipeHandle>(input->handle),
       input->version));
 }
 
-// TODO(yzshen): Unify StructTraits::Read*() methods and remove
-// HasReadFromDataViewMethod.
-template <typename T>
-struct HasReadFromDataViewMethod {
-  template <typename U>
-  static char Test(decltype(U::ReadFromDataView)*);
-  template <typename U>
-  static int Test(...);
-  static const bool value = sizeof(Test<T>(0)) == sizeof(char);
-
- private:
-  EnsureTypeIsComplete<T> check_t_;
-};
-
 template <typename T>
 struct HasIsNullMethod {
   template <typename U>
   static char Test(decltype(U::IsNull)*);
   template <typename U>
   static int Test(...);
   static const bool value = sizeof(Test<T>(0)) == sizeof(char);
 
  private:
   EnsureTypeIsComplete<T> check_t_;
 };
 
 template <
     typename Traits,
     typename UserType,
     typename std::enable_if<HasIsNullMethod<Traits>::value>::type* = nullptr>
 bool CallIsNullIfExists(const UserType& input) {
   return Traits::IsNull(input);
 }
 
 template <
     typename Traits,
     typename UserType,
     typename std::enable_if<!HasIsNullMethod<Traits>::value>::type* = nullptr>
 bool CallIsNullIfExists(const UserType& input) {
   return false;
 }
+template <typename T>
+struct HasSetToNullMethod {
+  template <typename U>
+  static char Test(decltype(U::SetToNull)*);
+  template <typename U>
+  static int Test(...);
+  static const bool value = sizeof(Test<T>(0)) == sizeof(char);
+
+ private:
+  EnsureTypeIsComplete<T> check_t_;
+};
+
+template <
+    typename Traits,
+    typename UserType,
+    typename std::enable_if<HasSetToNullMethod<Traits>::value>::type* = nullptr>
+bool CallSetToNullIfExists(UserType* output) {
+  Traits::SetToNull(output);
+  return true;
+}
+
+template <typename Traits,
+          typename UserType,
+          typename std::enable_if<!HasSetToNullMethod<Traits>::value>::type* =
+              nullptr>
+bool CallSetToNullIfExists(UserType* output) {
+  LOG(ERROR) << "A null value is received. But the Struct/Array/StringTraits "
+             << "class doesn't define a SetToNull() function and therefore is "
+             << "unable to deserialize the value.";
+  return false;
+}
 
 template <typename T>
 struct HasSetUpContextMethod {
   template <typename U>
   static char Test(decltype(U::SetUpContext)*);
   template <typename U>
   static int Test(...);
   static const bool value = sizeof(Test<T>(0)) == sizeof(char);
 
  private:
@@ skipping 53 matching lines @@
 ReturnType CallWithContext(ReturnType (*f)(ParamType),
                            MaybeConstUserType& input,
                            void* context) {
   return f(input);
 }
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_