Support script response files in GN.

tools/gn/functions_target.cc

Index: tools/gn/functions_target.cc
diff --git a/tools/gn/functions_target.cc b/tools/gn/functions_target.cc
index 79af5351b358ce2c87c1366718b6fb5d618b29ef..b04fea8b0f49d56c9121ac9b7432f27aad272751 100644
--- a/tools/gn/functions_target.cc
+++ b/tools/gn/functions_target.cc
@@ -108,6 +108,9 @@ const char kAction_Help[] =
     "  if an input file changes) by writing a depfile when the script is run\n"
     "  (see \"gn help depfile\"). This is more flexible than \"inputs\".\n"
     "\n"
+    "  If the command line length is very long, you can use response files\n"
+    "  to pass args to your script. See \"gn help response_file_contents\".\n"
+    "\n"
     "  It is recommended you put inputs to your script in the \"sources\"\n"
     "  variable, and stuff like other Python files required to run your\n"
     "  script in the \"inputs\" variable.\n"
@@ -127,8 +130,8 @@ const char kAction_Help[] =
     "\n"
     "Variables\n"
     "\n"
-    "  args, console, data, data_deps, depfile, deps, outputs*, script*,\n"
-    "  inputs, sources\n"
+    "  args, console, data, data_deps, depfile, deps, inputs, outputs*,\n"
+    "  response_file_contents, script*, sources\n"
     "  * = required\n"
     "\n"
     "Example\n"
@@ -182,6 +185,9 @@ const char kActionForEach_Help[] =
     "  listed in the \"inputs\" variable. These files are treated as\n"
     "  dependencies of each script invocation.\n"
     "\n"
+    "  If the command line length is very long, you can use response files\n"
+    "  to pass args to your script. See \"gn help response_file_contents\".\n"
+    "\n"
     "  You can dynamically write input dependencies (for incremental rebuilds\n"
     "  if an input file changes) by writing a depfile when the script is run\n"
     "  (see \"gn help depfile\"). This is more flexible than \"inputs\".\n"
@@ -198,8 +204,8 @@ const char kActionForEach_Help[] =
     "\n"
     "Variables\n"
     "\n"
-    "  args, console, data, data_deps, depfile, deps, outputs*, script*,\n"
-    "  inputs, sources*\n"
+    "  args, console, data, data_deps, depfile, deps, inputs, outputs*,\n"
+    "  response_file_contents, script*, sources*\n"
     "  * = required\n"
     "\n"
     "Example\n"