Support more configurability in GN toolchains

tools/gn/ninja_toolchain_writer_unittest.cc

+// 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.
+
+#include <sstream>
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "tools/gn/ninja_toolchain_writer.h"
+#include "tools/gn/test_with_scope.h"
+
+TEST(NinjaToolchainWriter, WriteToolRule) {
+  TestWithScope setup;
+
+  //Target target(setup.settings(), Label(SourceDir("//foo/"), "target"));
+  //target.set_output_type(Target::EXECUTABLE);
+  //target.SetToolchain(setup.toolchain());
+
+  std::ostringstream stream;
+
+  NinjaToolchainWriter writer(setup.settings(), setup.toolchain(),
+                              std::vector<const Target*>(), stream);
+  writer.WriteToolRule(Toolchain::TYPE_CC,
+                       setup.toolchain()->GetTool(Toolchain::TYPE_CC),
+                       std::string("prefix_"));
+
+  EXPECT_EQ(
+      "rule prefix_cc\n"
+      "  command = cc ${in} ${cflags} ${cflags_c} ${defines} ${include_dirs} "
+          "-o ${out}\n",
+      stream.str());
+}