Add more phony rules to GN build

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 a5787a2ebef41c1a25259b8c84b6cf79072b3073..0bc266dc5873b0dab9d6979dd7483327d955efff 100644
--- a/tools/gn/filesystem_utils.cc
+++ b/tools/gn/filesystem_utils.cc
@@ -313,6 +313,23 @@ base::StringPiece FindDir(const std::string* path) {
   return base::StringPiece(path->data(), filename_offset);
 }
 
+base::StringPiece FindLastDirComponent(const SourceDir& dir) {
+  const std::string& dir_string = dir.value();
+
+  if (dir_string.empty())
+    return base::StringPiece();
+  int cur = static_cast<int>(dir_string.size()) - 1;
+  DCHECK(dir_string[cur] == '/');
+  int end = cur;
+  cur--;  // Skip before the last slash.
+
+  for (; cur >= 0; cur--) {
+    if (dir_string[cur] == '/')
+      return base::StringPiece(&dir_string[cur + 1], end - cur - 1);
+  }
+  return base::StringPiece(&dir_string[0], end);
+}
+
 bool EnsureStringIsInOutputDir(const SourceDir& dir,
                                const std::string& str,
                                const Value& originating,