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Creates a new header TraceWrapperBase.h and makes ScriptWrappable.h
and TraceWrapperMember.h include TraceWrapperBase.h that defines
TraceWrapperBase class.

Bug: 
Change-Id: I9135b9394ef4a116322d6f9fc1ac97969e4735f3
Reviewed-on: https://chromium-review.googlesource.com/664503Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501603}