[Image Fetcher] Move image_decoder_impl under c/b/image_fetcher

This class was added under search/suggestions for convenience. Now
that we have the image_fetcher directory, moving it there as the
decoder is logically associated with image fetching.

Bug: 624761
Change-Id: Ie5356cf784c68e73a955df8352534fd6d8bbc450
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1542497
Commit-Queue: Brandon Wylie <[email protected]>
Reviewed-by: Marc Treib <[email protected]>
Reviewed-by: Sky Malice <[email protected]>
Cr-Commit-Position: refs/heads/master@{#649349}
21 files changed