Add a mojo struct corresponding and typemapped to base::File.

mojo/common/common_custom_types_struct_traits.h

Index: mojo/common/common_custom_types_struct_traits.h
diff --git a/mojo/common/common_custom_types_struct_traits.h b/mojo/common/common_custom_types_struct_traits.h
index b99e15ffc9d803ff7e0aea30cfc60d671f01b007..39a424fac5152561b0d6273c752b564706319eaf 100644
--- a/mojo/common/common_custom_types_struct_traits.h
+++ b/mojo/common/common_custom_types_struct_traits.h
@@ -5,6 +5,7 @@
 #ifndef MOJO_COMMON_COMMON_CUSTOM_TYPES_STRUCT_TRAITS_H_
 #define MOJO_COMMON_COMMON_CUSTOM_TYPES_STRUCT_TRAITS_H_
 
+#include "base/files/file.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/unguessable_token.h"
 #include "base/version.h"
@@ -68,6 +69,16 @@ struct StructTraits<common::mojom::TimeDeltaDataView, base::TimeDelta> {
   }
 };
 
+template <>
+struct StructTraits<common::mojom::FileDataView, base::File> {
+  static bool IsNull(const base::File& file) { return !file.IsValid(); }
+
+  static void SetToNull(base::File* file) { *file = base::File(); }
+
+  static mojo::ScopedHandle fd(base::File& file);

[dcheng, 2016/11/28 17:25:07]

Nit: const

[Sam McNally, 2016/11/28 21:21:47]

It has to be non-const to TakePlatformFile().

+  static bool Read(common::mojom::FileDataView data, base::File* file);
+};
+
 }  // namespace mojo
 
 #endif  // MOJO_COMMON_COMMON_CUSTOM_TYPES_STRUCT_TRAITS_H_