[NTP Snippets] Cleanups from clang-tidy

components/ntp_snippets/content_suggestions_provider.cc

 // Copyright 2016 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 "components/ntp_snippets/content_suggestions_provider.h"
 
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "components/ntp_snippets/category_factory.h"
 
 namespace ntp_snippets {
 
 namespace {
 
 const char kCombinedIDFormat[] = "%d|%s";
 const char kSeparator = '|';
 
 }  // namespace
 
 ContentSuggestionsProvider::ContentSuggestionsProvider(
     Observer* observer,
     CategoryFactory* category_factory)
     : observer_(observer), category_factory_(category_factory) {}
 
-ContentSuggestionsProvider::~ContentSuggestionsProvider() {}
+ContentSuggestionsProvider::~ContentSuggestionsProvider() = default;
 
 std::string ContentSuggestionsProvider::MakeUniqueID(
     Category category,
     const std::string& within_category_id) const {
   return base::StringPrintf(kCombinedIDFormat, category.id(),
                             within_category_id.c_str());
 }
 
 Category ContentSuggestionsProvider::GetCategoryFromUniqueID(
     const std::string& unique_id) const {
   size_t colon_index = unique_id.find(kSeparator);
   DCHECK_NE(std::string::npos, colon_index) << "Not a valid unique_id: "
                                             << unique_id;
   int category = -1;
   bool ret = base::StringToInt(unique_id.substr(0, colon_index), &category);
   DCHECK(ret) << "Non-numeric category part in unique_id: " << unique_id;
   return category_factory_->FromIDValue(category);
 }
 
 std::string ContentSuggestionsProvider::GetWithinCategoryIDFromUniqueID(
     const std::string& unique_id) const {
   size_t colon_index = unique_id.find(kSeparator);
   DCHECK_NE(std::string::npos, colon_index) << "Not a valid unique_id: "
                                             << unique_id;
   return unique_id.substr(colon_index + 1);
 }
 
 }  // namespace ntp_snippets