[remoting android] Make Android credits a GN template.

remoting/credits/credits.gni

+# Copyright 2017 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.
+
+# Generates a credits HTML file, based on the third-party dependencies of
+# a provided GN target.
+# Parameters:
+#   gn_target: The target whose dependencies should be listed in the credits.
+#   credits_gen_dir: Directory (without trailing slash) where the generated
+#     HTML will be placed, together with the copied JSS+CS files.
+template("remoting_credits") {
+  _credits_source_dir = "//remoting/credits"
+
+  action("${target_name}__generate") {
+    # Generate credits.html in a temporary location, so it can be copied into
+    # the final location - see comment for 'copy' target.
+    _credits_html_file = "$target_gen_dir/$target_name/credits.html"
+    _credits_template = "$_credits_source_dir/credits.tmpl"
+    _credits_entry_template = "$_credits_source_dir/credits_entry.tmpl"
+    script = "//tools/licenses.py"
+    depfile = "$target_gen_dir/$target_name.d"
+    inputs = [
+      _credits_template,
+      _credits_entry_template,
+    ]
+    outputs = [
+      _credits_html_file,
+    ]
+    args = [
+      "credits",
+      rebase_path(_credits_html_file, root_build_dir),
+      "--file-template",
+      rebase_path(_credits_template, root_build_dir),
+      "--entry-template",
+      rebase_path(_credits_entry_template, root_build_dir),
+      "--depfile",
+      rebase_path(depfile, root_build_dir),
+      "--gn-target",
+      invoker.gn_target,
+      "--gn-out-dir",
+      rebase_path(root_build_dir),
+    ]
+  }
+
+  # This target purposefully copies the generated HTML file (instead of
+  # directly generating the HTML file into credits_gen_dir), so that the caller
+  # can use get_target_outputs(:target_name) and the HTML file will be
+  # included in the returned list along with the JS+CSS files.
+  copy(target_name) {
+    _generate_target = ":${target_name}__generate"
+    _credits_gen_dir = invoker.credits_gen_dir
+    sources = [
+                "$_credits_source_dir/credits_css.css",
+                "$_credits_source_dir/credits_js.js",
+              ] + get_target_outputs(_generate_target)
+    outputs = [
+      "$_credits_gen_dir/{{source_file_part}}",
+    ]
+    deps = [
+      _generate_target,
+    ]
+  }
+}