Add missing header files to GN files

third_party/snappy/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 
 config("snappy_config") {
   include_dirs = [ "src" ]
 
   # These OS-specific generated headers were made by running the configure
@@ skipping 25 matching lines @@
   sources = [
     "src/snappy-internal.h",
     "src/snappy-sinksource.cc",
     "src/snappy-sinksource.h",
     "src/snappy-stubs-internal.cc",
     "src/snappy-stubs-internal.h",
     "src/snappy.cc",
     "src/snappy.h",
   ]
 
+  if (is_win) {
+    sources += [ "win32/snappy-stubs-public.h" ]
+  } else if (is_mac) {
+    sources += [ "mac/snappy-stubs-public.h" ]
+  } else {
+    sources += [ "linux/snappy-stubs-public.h" ]
+  }
+
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     "//build/config/compiler:no_chromium_code",
 
     # Must be after no_chromium_code for warning flags to be ordered correctly.
     ":snappy_warnings",
   ]
   public_configs = [ ":snappy_config" ]
 
   # Chromium doesn't use automake, but we generated config.h offline for all the
   # platforms that we build for.
   defines = [ "HAVE_CONFIG_H" ]
 }