Support spaces in Mac GN build output names.

tools/gn/substitution_writer_unittest.cc

Index: tools/gn/substitution_writer_unittest.cc
diff --git a/tools/gn/substitution_writer_unittest.cc b/tools/gn/substitution_writer_unittest.cc
index 6ae28ec0150c27bcfc50f3133ae648d16a831275..5abd61929e997084caa970ef2f6e091054a4d694 100644
--- a/tools/gn/substitution_writer_unittest.cc
+++ b/tools/gn/substitution_writer_unittest.cc
@@ -193,6 +193,10 @@ TEST(SubstitutionWriter, TargetSubstitutions) {
   EXPECT_EQ("//foo/bar:baz", result);
 
   EXPECT_TRUE(SubstitutionWriter::GetTargetSubstitution(
+      &target, SUBSTITUTION_LABEL_NAME, &result));
+  EXPECT_EQ("baz", result);
+
+  EXPECT_TRUE(SubstitutionWriter::GetTargetSubstitution(
       &target, SUBSTITUTION_ROOT_GEN_DIR, &result));
   EXPECT_EQ("gen", result);