Using a flat_set to get rid of const_cast.

TemplateURLSet should be small enougth to use flat_set.
When implementing flat_sets, we specificly desided to provide a different
solution for Librayr Working Group issue: #2059, which allows to just
remove the const_cast.

Here is a test for it:
https://cs.chromium.org/chromium/src/base/containers/flat_tree_unittest.cc?sq=package:chromium&l=962

Change-Id: I4dfd5f3a5510c11ca4ef325dd0cb1e74fc7735f4
Reviewed-on: https://chromium-review.googlesource.com/995279Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Denis Yaroshevskiy <dyaroshev@yandex-team.ru>
Cr-Commit-Position: refs/heads/master@{#548031}

components/search_engines/search_host_to_urls_map.cc

@@ -45,8 +45,7 @@ void SearchHostToURLsMap::Remove(const TemplateURL* template_url) {
   auto set_with_url =
       std::find_if(host_to_urls_map_.begin(), host_to_urls_map_.end(),
                    [&](std::pair<const std::string, TemplateURLSet>& entry) {
-                     return entry.second.erase(
-                         const_cast<TemplateURL*>(template_url));
+                     return entry.second.erase(template_url);
                    });
 
   if (set_with_url != host_to_urls_map_.end() && set_with_url->second.empty())

components/search_engines/search_host_to_urls_map.h

@@ -7,9 +7,9 @@
 
 #include <functional>
 #include <map>
-#include <set>
 #include <string>
 
+#include "base/containers/flat_set.h"
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
 #include "components/search_engines/template_url_service.h"
@@ -19,7 +19,7 @@
 // caller to ensure the right lifetime of them.
 class SearchHostToURLsMap {
  public:
-  typedef std::set<TemplateURL*> TemplateURLSet;
+  using TemplateURLSet = base::flat_set<TemplateURL*>;
 
   SearchHostToURLsMap();
   ~SearchHostToURLsMap();