Add initial prototype for the GN meta-buildsystem.

tools/gn/command_gen.cc

Index: tools/gn/command_gen.cc
diff --git a/tools/gn/command_gen.cc b/tools/gn/command_gen.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ab64a8d5c72150c5f6e2ff672e862c2d4e594023
--- /dev/null
+++ b/tools/gn/command_gen.cc
@@ -0,0 +1,66 @@
+// Copyright (c) 2013 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 "base/bind.h"
+#include "base/command_line.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/time/time.h"
+#include "tools/gn/build_settings.h"
+#include "tools/gn/commands.h"
+#include "tools/gn/ninja_target_writer.h"
+#include "tools/gn/ninja_writer.h"
+#include "tools/gn/scheduler.h"
+#include "tools/gn/setup.h"
+#include "tools/gn/standard_out.h"
+
+namespace {
+
+// Suppress output on success.
+const char kSwitchQuiet[] = "q";
+
+}  // namespace
+
+int RunGenCommand(const std::vector<std::string>& args) {
+  base::TimeTicks begin_time = base::TimeTicks::Now();
+
+  // Deliberately leaked to avoid expensive process teardown.
+  Setup* setup = new Setup;
+  if (!setup->DoSetup())
+    return 1;
+
+  // Cause the load to also generate the ninja files for each target.
+  setup->build_settings().set_target_resolved_callback(
+      base::Bind(&NinjaTargetWriter::RunAndWriteFile));
+
+  // Do the actual load. This will also write out the target ninja files.
+  if (!setup->Run())
+    return 1;
+
+  // Write the root ninja files.
+  if (!NinjaWriter::RunAndWriteFiles(&setup->build_settings())) {
+    Err(Location(),
+        "Couldn't open root buildfile(s) for writing").PrintToStdout();
+    return 1;
+  }
+
+  base::TimeTicks end_time = base::TimeTicks::Now();
+
+  if (!CommandLine::ForCurrentProcess()->HasSwitch(kSwitchQuiet)) {
+    OutputString("Done. ", DECORATION_GREEN);
+
+    // TODO(brettw) get the number of targets without getting the entire list.
+    std::vector<const Target*> all_targets;
+    setup->build_settings().target_manager().GetAllTargets(&all_targets);
+    std::string stats = "Generated " +
+        base::IntToString(static_cast<int>(all_targets.size())) +
+        " targets from " +
+        base::IntToString(
+            setup->scheduler().input_file_manager()->GetInputFileCount()) +
+        " files in " +
+        base::IntToString((end_time - begin_time).InMilliseconds()) + "ms\n";
+    OutputString(stats);
+  }
+
+  return 0;
+}