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- Implements the move constructor and assignment operator to zero
  bytes_size_ and storage_type_. Otherwise clients checking for empty
  BigBuffers by examining the size() may try to use an empty
  BigBuffer (where data() == nullptr).

Bug: chromium:992991
Change-Id: I23c8d8db35de76762606ecd488cbebfe1ac42ae9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1803136Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697329}