Factor and simplify generation of the lookup trie used for HTMLLookupTrie.

third_party/WebKit/Source/build/scripts/scripts.gni

Index: third_party/WebKit/Source/build/scripts/scripts.gni
diff --git a/third_party/WebKit/Source/build/scripts/scripts.gni b/third_party/WebKit/Source/build/scripts/scripts.gni
index 5fd015eab4e6bdb700120e01cc0a1fdf5c177ef5..edb1937a579ccd241fd10b0488a646fe2072bd20 100644
--- a/third_party/WebKit/Source/build/scripts/scripts.gni
+++ b/third_party/WebKit/Source/build/scripts/scripts.gni
@@ -56,6 +56,9 @@ make_element_type_helpers_files =
       "$_scripts_dir/templates/ElementTypeHelpers.h.tmpl",
     ]
 
+make_trie_helpers_files =
+    scripts_for_in_files + [ "$_scripts_dir/trie_builder.py" ]
+
 # The executables are relative to the build directory. Don't rebase it because
 # on Posix we want to run the system one on the path.
 if (host_os == "win") {