Improve GN handling of directory templates.

tools/gn/ninja_copy_target_writer_unittest.cc

Index: tools/gn/ninja_copy_target_writer_unittest.cc
diff --git a/tools/gn/ninja_copy_target_writer_unittest.cc b/tools/gn/ninja_copy_target_writer_unittest.cc
index 0b1618e15e58164ae750a90b7c80da3f0ca66ef9..e9f24371ba27db5c35399d25c7b6ff17076b4c04 100644
--- a/tools/gn/ninja_copy_target_writer_unittest.cc
+++ b/tools/gn/ninja_copy_target_writer_unittest.cc
@@ -22,7 +22,7 @@ TEST(NinjaCopyTargetWriter, Run) {
   target.sources().push_back(SourceFile("//foo/input2.txt"));
 
   target.action_values().outputs().push_back(
-      SourceFile("//out/Debug/{{source_name_part}}.out"));
+      "//out/Debug/{{source_name_part}}.out");
 
   std::ostringstream out;
   NinjaCopyTargetWriter writer(&target, setup.toolchain(), out);
@@ -56,8 +56,7 @@ TEST(NinjaCopyTargetWriter, ToolchainDeps) {
 
   target.sources().push_back(SourceFile("//foo/input1.txt"));
 
-  target.action_values().outputs().push_back(
-      SourceFile("//out/Debug/output.out"));
+  target.action_values().outputs().push_back("//out/Debug/output.out");
 
   std::ostringstream out;
   NinjaCopyTargetWriter writer(&target, setup.toolchain(), out);