Mojo cpp bindings: remove IsNonNullableValidationEnabled() check

mojo/public/cpp/bindings/lib/validation_errors.h

 // Copyright 2014 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_VALIDATION_ERRORS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_
 
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
@@ skipping 70 matching lines @@
 
   ValidationError last_warning() const { return last_warning_; }
   void set_last_warning(ValidationError error) { last_warning_ = error; }
 
  private:
   ValidationError last_warning_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(SerializationWarningObserverForTesting);
 };
 
-// Currently it only returns true during validation and serialization tests.
-//
-// TODO(yzshen): Remove this function and enable non-nullable validation by
-// default.
-bool IsNonNullableValidationEnabled();
-
 }  // namespace internal
 }  // namespace mojo
 
 // In debug build, logs a serialization warning if |condition| evaluates to
 // true:
 //   - if there is a SerializationWarningObserverForTesting object alive,
 //     records |error| in it;
 //   - otherwise, logs a fatal-level message.
 // |error| is the validation error that will be triggered by the receiver
 // of the serialzation result.
 //
 // In non-debug build, does nothing (not even compiling |condition|).
 #define MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(condition, error) \
     MOJO_DLOG_IF(FATAL, (condition) && !ReportSerializationWarning(error)) \
         << "The outgoing message will trigger " \
         << ValidationErrorToString(error) << " at the receiving side.";
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_