Add a preference to control Windows desktop search redirection.

components/search_engines/search_engines_switches.cc

Index: components/search_engines/search_engines_switches.cc
diff --git a/components/search_engines/search_engines_switches.cc b/components/search_engines/search_engines_switches.cc
index f15afa7a0261908411118f2bccc97f3325fab517..190662c08f52d18a002d98de9cea2074f49e50a4 100644
--- a/components/search_engines/search_engines_switches.cc
+++ b/components/search_engines/search_engines_switches.cc
@@ -10,10 +10,4 @@ namespace switches {
 // testing.
 const char kExtraSearchQueryParams[] = "extra-search-query-params";
 
-#if defined(OS_WIN)
-// Use the default search provider for desktop search.
-const char kUseDefaultSearchProviderForDesktopSearch[] =
-    "use-default-search-provider-for-desktop-search";
-#endif  // defined(OS_WIN)
-
 }  // namespace switches