Closure compile JS files with GYP.

third_party/closure_compiler/compile_js.gypi

+# Copyright 2014 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.
+{
+  'type': 'none',
+  'variables': {
+    'CLOSURE_DIR': '<(DEPTH)/third_party/closure_compiler',
+  },
+  'actions': [
+    {
+      # This action optionally takes these arguments:
+      # - depends: scripts that the source file depends on being included already
+      # - externs: files that describe globals used by |source|
+      'action_name': 'compile_js',
+      'variables': {
+        'source_file': '<(_target_name).js',
+        'out_file': '<(SHARED_INTERMEDIATE_DIR)/closure/<!(python <(CLOSURE_DIR)/build/outputs.py <@(source_file))',
+        'externs%': [],
+        'depends%': [],
+      },
+      'inputs': [
+        '<(CLOSURE_DIR)/checker.py',
+        '<(CLOSURE_DIR)/processor.py',
+        '<(CLOSURE_DIR)/build/inputs.py',
+        '<(CLOSURE_DIR)/build/outputs.py',
+        '<(CLOSURE_DIR)/compiler/compiler.jar',
+        '<(CLOSURE_DIR)/runner/runner.jar',
+        '<!@(python <(CLOSURE_DIR)/build/inputs.py <(source_file) -d <@(depends) -e <@(externs))',
+      ],
+      'outputs': [
+        '<(out_file)',
+      ],
+      'action': [
+        'python',
+        '<(CLOSURE_DIR)/checker.py',
+        '<(source_file)',
+        '--depends', '<@(depends)',
+        '--externs', '<@(externs)',
+        '--out_file', '<(out_file)',
+      ],
+      'message': 'Compiling <(source_file)',
+    }
+  ],
+}