Handle |public| in check_gn_headers.py

If |public| of a target contains files, count them as recognized
headers as well.

BUG=661774

Review-Url: https://codereview.chromium.org/2841323003
Cr-Commit-Position: refs/heads/master@{#467826}
diff --git a/build/check_gn_headers_unittest.py b/build/check_gn_headers_unittest.py
index f62fe62..892fa66 100755
--- a/build/check_gn_headers_unittest.py
+++ b/build/check_gn_headers_unittest.py
@@ -38,8 +38,14 @@
       "//:All": {
       },
       "//:base": {
+         "public": [ "//base/p.h" ],
          "sources": [ "//base/a.cc", "//base/a.h", "//base/b.hh" ],
          "visibility": [ "*" ]
+      },
+      "//:star_public": {
+         "public": "*",
+         "sources": [ "//base/c.h" ],
+         "visibility": [ "*" ]
       }
     }
 }
@@ -88,6 +94,8 @@
     expected = set([
         'base/a.h',
         'base/b.hh',
+        'base/c.h',
+        'base/p.h',
     ])
     self.assertEquals(headers, expected)