Add more phony rules to GN build

tools/gn/filesystem_utils_unittest.cc

Index: tools/gn/filesystem_utils_unittest.cc
diff --git a/tools/gn/filesystem_utils_unittest.cc b/tools/gn/filesystem_utils_unittest.cc
index 3416e1659fca2e637f75b8339d1f390223d641b7..ec1a53e7633d04d11d67f9c662a403af830dadac 100644
--- a/tools/gn/filesystem_utils_unittest.cc
+++ b/tools/gn/filesystem_utils_unittest.cc
@@ -73,6 +73,23 @@ TEST(FilesystemUtils, FindDir) {
   EXPECT_EQ("foo/bar/", FindDir(&input));
 }
 
+TEST(FilesystemUtils, FindLastDirComponent) {
+  SourceDir empty;
+  EXPECT_EQ("", FindLastDirComponent(empty));
+
+  SourceDir root("/");
+  EXPECT_EQ("", FindLastDirComponent(root));
+
+  SourceDir srcroot("//");
+  EXPECT_EQ("", FindLastDirComponent(srcroot));
+
+  SourceDir regular1("//foo/");
+  EXPECT_EQ("foo", FindLastDirComponent(regular1));
+
+  SourceDir regular2("//foo/bar/");
+  EXPECT_EQ("bar", FindLastDirComponent(regular2));
+}
+
 TEST(FilesystemUtils, IsPathAbsolute) {
   EXPECT_TRUE(IsPathAbsolute("/foo/bar"));
   EXPECT_TRUE(IsPathAbsolute("/"));