Make V8 extras a separate type of native

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 233499b71025ebfa04fb9171015f7c44fdf3a19f..be1e76c0c26fbddf72f49a4cd8fdb174a43cf47d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -295,6 +295,36 @@ action("js2c_experimental") {
   }
 }
 
+action("js2c_extras") {
+  visibility = [ ":*" ]  # Only targets in this file can depend on this.
+
+  script = "tools/js2c.py"
+
+  # The script depends on this other script, this rule causes a rebuild if it
+  # changes.
+  inputs = [ "tools/jsmin.py" ]
+
+  sources = v8_extra_library_files
+
+  outputs = [
+    "$target_gen_dir/extras-libraries.cc",
+  ]
+
+  args = [
+           rebase_path("$target_gen_dir/extras-libraries.cc",
+                       root_build_dir),
+           "EXTRAS",
+         ] + rebase_path(sources, root_build_dir)
+
+  if (v8_use_external_startup_data) {
+    outputs += [ "$target_gen_dir/libraries_extras.bin" ]
+    args += [
+      "--startup_blob",
+      rebase_path("$target_gen_dir/libraries_extras.bin", root_build_dir),
+    ]
+  }
+}
+
 action("d8_js2c") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
 
@@ -320,11 +350,13 @@ if (v8_use_external_startup_data) {
     deps = [
       ":js2c",
       ":js2c_experimental",
+      ":js2c_extras",
     ]
 
     sources = [
       "$target_gen_dir/libraries.bin",
       "$target_gen_dir/libraries_experimental.bin",
+      "$target_gen_dir/libraries_extras.bin",
     ]
 
     outputs = [
@@ -404,12 +436,14 @@ source_set("v8_nosnapshot") {
   deps = [
     ":js2c",
     ":js2c_experimental",
+    ":js2c_extras",
     ":v8_base",
   ]
 
   sources = [
     "$target_gen_dir/libraries.cc",
     "$target_gen_dir/experimental-libraries.cc",
+    "$target_gen_dir/extras-libraries.cc",
     "src/snapshot/snapshot-empty.cc",
   ]
 
@@ -428,6 +462,7 @@ source_set("v8_snapshot") {
   deps = [
     ":js2c",
     ":js2c_experimental",
+    ":js2c_extras",
     ":run_mksnapshot",
     ":v8_base",
   ]
@@ -435,6 +470,7 @@ source_set("v8_snapshot") {
   sources = [
     "$target_gen_dir/libraries.cc",
     "$target_gen_dir/experimental-libraries.cc",
+    "$target_gen_dir/extras-libraries.cc",
     "$target_gen_dir/snapshot.cc",
   ]
 
@@ -454,6 +490,7 @@ if (v8_use_external_startup_data) {
     deps = [
       ":js2c",
       ":js2c_experimental",
+      ":js2c_extras",
       ":run_mksnapshot",
       ":v8_base",
       ":natives_blob",