Add directory extraction to GN path handling.

tools/gn/function_get_path_info_unittest.cc

Index: tools/gn/function_get_path_info_unittest.cc
diff --git a/tools/gn/function_get_path_info_unittest.cc b/tools/gn/function_get_path_info_unittest.cc
index 12bdc2a5adab7a0dced4433ccac8d30d8e1ec71b..1756c0c3f4c84a81e7e2fbfad4416f3f56a21dee 100644
--- a/tools/gn/function_get_path_info_unittest.cc
+++ b/tools/gn/function_get_path_info_unittest.cc
@@ -87,3 +87,25 @@ TEST_F(GetPathInfoTest, AbsPath) {
   EXPECT_EQ("/foo/", Call("/foo/", "abspath"));
   EXPECT_EQ("/", Call("/", "abspath"));
 }
+
+// Note build dir is "//out/Debug/".
+TEST_F(GetPathInfoTest, OutDir) {
+  EXPECT_EQ("//out/Debug/obj/src/foo/foo", Call("foo/bar.txt", "out_dir"));
+  EXPECT_EQ("//out/Debug/obj/src/foo/bar", Call("bar/", "out_dir"));
+  EXPECT_EQ("//out/Debug/obj/src/foo", Call(".", "out_dir"));
+  EXPECT_EQ("//out/Debug/obj/src/foo", Call("bar", "out_dir"));
+  EXPECT_EQ("//out/Debug/obj/foo", Call("//foo/bar.txt", "out_dir"));
+  // System paths go into the root obj directory.
+  EXPECT_EQ("//out/Debug/obj", Call("/foo/bar.txt", "out_dir"));
+}
+
+// Note build dir is "//out/Debug/".
+TEST_F(GetPathInfoTest, GenDir) {
+  EXPECT_EQ("//out/Debug/gen/src/foo/foo", Call("foo/bar.txt", "gen_dir"));
+  EXPECT_EQ("//out/Debug/gen/src/foo/bar", Call("bar/", "gen_dir"));
+  EXPECT_EQ("//out/Debug/gen/src/foo", Call(".", "gen_dir"));
+  EXPECT_EQ("//out/Debug/gen/src/foo", Call("bar", "gen_dir"));
+  EXPECT_EQ("//out/Debug/gen/foo", Call("//foo/bar.txt", "gen_dir"));
+  // System paths go into the root obj directory.
+  EXPECT_EQ("//out/Debug/gen", Call("/foo/bar.txt", "gen_dir"));
+}