Support script response files in GN.

tools/gn/function_write_file.cc

Index: tools/gn/function_write_file.cc
diff --git a/tools/gn/function_write_file.cc b/tools/gn/function_write_file.cc
index d24abc159ac5270046cf7a915b9bac70edea0163..02acca423f2f3b4dad374b4958b8c1070bacae76 100644
--- a/tools/gn/function_write_file.cc
+++ b/tools/gn/function_write_file.cc
@@ -82,10 +82,15 @@ const char kWriteFile_Help[] =
     "  written, the file will not be updated. This will prevent unnecessary\n"
     "  rebuilds of targets that depend on this file.\n"
     "\n"
+    "  One use for write_file is to write a list of inputs to an script\n"
+    "  that might be too long for the command line. However, it is\n"
+    "  preferrable to use response files for this purpose. See\n"
+    "  \"gn help response_file_contents\".\n"
+    "\n"
     "  TODO(brettw) we probably need an optional third argument to control\n"
     "  list formatting.\n"
     "\n"
-    "Arguments:\n"
+    "Arguments\n"
     "\n"
     "  filename\n"
     "      Filename to write. This must be within the output directory.\n"