Add Go build support for GN.

build/go/rules.gni

+# 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.
+
+declare_args() {
+  # By default, there is no go build tool, because go builds are not supported.
+  go_build_tool = ""
+}
+
+template("go_test_binary") {
+  # Only available on linux for now.
+  assert(is_linux)
+  assert(defined(invoker.sources))
+#  assert(defined(invoker.go_base_module))
+  assert(go_build_tool != "")
+
+  action(target_name) {
+    script = "//build/go/go.py"
+    outputs = [ "${target_out_dir}/${target_name}" ]
+    # Since go test does not permit specifying an output directory or output
+    # binary name, we create a temporary build directory, and the python
+    # script will later identify the output, copy it to the target location,
+    # and clean up the temporary build directory.
+    build_dir = "${target_out_dir}/${target_name}_build"
+    args = [
+      "${go_build_tool}",
+      rebase_path(build_dir, root_build_dir),
+      rebase_path(target_out_dir, root_build_dir) + "/${target_name}",
+      rebase_path("//", root_build_dir),
+      "-I" + rebase_path("//", "//"),
+      "-L" + rebase_path("//out/Release/lib", "//") +
+      " -lmojo_system_impl -lbase",
+      "test", "-c",
+    ] + rebase_path(invoker.sources, build_dir)
+  }
+}