Check system-include dependencies in GN

tools/gn/c_include_iterator_unittest.cc

Index: tools/gn/c_include_iterator_unittest.cc
diff --git a/tools/gn/c_include_iterator_unittest.cc b/tools/gn/c_include_iterator_unittest.cc
index a4278b21200b15a68567cafda1d632c00651263c..80e34e0c8f301a951d9033155c0f96cef0da38ee 100644
--- a/tools/gn/c_include_iterator_unittest.cc
+++ b/tools/gn/c_include_iterator_unittest.cc
@@ -49,6 +49,10 @@ TEST(CIncludeIterator, Basic) {
   EXPECT_TRUE(RangeIs(range, 3, 11, 20)) << range.begin().Describe(true);
 
   EXPECT_TRUE(iter.GetNextIncludeString(&contents, &range));
+  EXPECT_EQ("stdio.h", contents);
+  EXPECT_TRUE(RangeIs(range, 5, 11, 18)) << range.begin().Describe(true);
+
+  EXPECT_TRUE(iter.GetNextIncludeString(&contents, &range));
   EXPECT_EQ("foo/baz.h", contents);
   EXPECT_TRUE(RangeIs(range, 7, 12, 21)) << range.begin().Describe(true);