Add GN function get_label_info

tools/gn/filesystem_utils.cc

Index: tools/gn/filesystem_utils.cc
diff --git a/tools/gn/filesystem_utils.cc b/tools/gn/filesystem_utils.cc
index 6279964914f96f150eeea9baed64b361c143fcf2..9140f80660e94f69abdf7d667bcc4cb1d372f9e2 100644
--- a/tools/gn/filesystem_utils.cc
+++ b/tools/gn/filesystem_utils.cc
@@ -667,6 +667,16 @@ SourceDir SourceDirForCurrentDirectory(const base::FilePath& source_root) {
   return SourceDirForPath(source_root, cd);
 }
 
+std::string GetOutputSubdirName(const Label& toolchain_label, bool is_default) {
+  // The default toolchain has no subdir.
+  if (is_default)
+    return std::string();
+
+  // For now just assume the toolchain name is always a valid dir name. We may
+  // want to clean up the in the future.
+  return toolchain_label.name() + "/";
+}
+
 SourceDir GetToolchainOutputDir(const Settings* settings) {
   const OutputFile& toolchain_subdir = settings->toolchain_output_subdir();
 
@@ -677,6 +687,13 @@ SourceDir GetToolchainOutputDir(const Settings* settings) {
   return SourceDir(SourceDir::SWAP_IN, &result);
 }
 
+SourceDir GetToolchainOutputDir(const BuildSettings* build_settings,
+                                const Label& toolchain_label, bool is_default) {
+  std::string result = build_settings->build_dir().value();
+  result.append(GetOutputSubdirName(toolchain_label, is_default));
+  return SourceDir(SourceDir::SWAP_IN, &result);
+}
+
 SourceDir GetToolchainGenDir(const Settings* settings) {
   const OutputFile& toolchain_subdir = settings->toolchain_output_subdir();
 
@@ -688,6 +705,14 @@ SourceDir GetToolchainGenDir(const Settings* settings) {
   return SourceDir(SourceDir::SWAP_IN, &result);
 }
 
+SourceDir GetToolchainGenDir(const BuildSettings* build_settings,
+                             const Label& toolchain_label, bool is_default) {
+  std::string result = GetToolchainOutputDir(
+      build_settings, toolchain_label, is_default).value();
+  result.append("gen/");
+  return SourceDir(SourceDir::SWAP_IN, &result);
+}
+
 SourceDir GetOutputDirForSourceDir(const Settings* settings,
                                    const SourceDir& source_dir) {
   SourceDir toolchain = GetToolchainOutputDir(settings);