[Closure Externs] Generate closure compiler externs as part of compile

tools/json_schema_compiler/externs.gni

Index: tools/json_schema_compiler/externs.gni
diff --git a/tools/json_schema_compiler/externs.gni b/tools/json_schema_compiler/externs.gni
new file mode 100644
index 0000000000000000000000000000000000000000..f3e21248e93c69a4ce8137cd239aea26216d1166
--- /dev/null
+++ b/tools/json_schema_compiler/externs.gni
@@ -0,0 +1,55 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+template("closure_externs") {
+  assert(defined(invoker.sources),
+         "\"sources\" must be defined for the $target_name template.")
+  print("running closure")
+
+  compiler_root = "//tools/json_schema_compiler"
+  compiler_script = "$compiler_root/compiler.py"
+  compiler_sources = [
+    "$compiler_root/code.py",
+    "$compiler_root/compiler.py",
+    "$compiler_root/idl_schema.py",
+    "$compiler_root/js_externs_generator.py",
+    "$compiler_root/model.py",
+  ]
+
+  action_name = "${target_name}_externs"
+  action_foreach(action_name) {
+    print("running")
+    print("gen: " + root_gen_dir)
+    print("build: " + root_build_dir)
+    print("source name: {{source_name_part}}")
+    foreach(i, invoker.sources) {
+      print(i)
+    }
+    sources = invoker.sources
+    script = compiler_script
+    inputs = compiler_sources
+    outputs = [
+      "$target_gen_dir/{{source_name_part}}.js",
+    ]
+    print("outputs")
+    foreach(o, outputs) {
+      print(o)
+    }
+    args = [
+      "{{source}}",
+      "--root=" + rebase_path("//", root_build_dir),
+      "--destdir=" + rebase_path(root_gen_dir, root_build_dir),
+      "--output-dir=third_party/closure_compiler/externs",
+      "--generator=externs",
+    ]
+  }
+
+  source_set(target_name) {
+    sources = invoker.sources
+    if (!defined(public_deps)) {
+      public_deps = []
+    }
+    public_deps += [ ":$action_name" ]
+  }
+}