Set same type nullable to typemap of scoped_refptr<ResourceRequestBody>

This is a cleanup of https://crrev.com/c/1367365. nullable_is_same_type is well
suited for typemapping to scoped_refptr<>.

Bug: 911930
Change-Id: Iff6800eb000ebaf84b109e5989f4c2dd192f1503
Reviewed-on: https://chromium-review.googlesource.com/c/1415236
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623626}
5 files changed