Cache Storage: Move files to content/*/cache_storage, rename classes

* Introduce content/*/cache_storage
* Move Cache Storage files from content/*/service_worker
* Update gypi/gn files
* Rename classes, ipc messages, protobuf messages

The renames are basically mechanical:
* ServiceWorkerCacheStorageFoo -> CacheStorageFoo
* ServiceWorkerCacheFoo -> CacheStorageFoo
* ServiceWorkerCache -> CacheStorageCache (not just 'Cache')

Also, made jkarlin@ and jsbell@ (that's me!) OWNERS in the new
directories in addition to the */service_worker/OWNERS.

BUG=439389

Review URL: https://codereview.chromium.org/1039763002

Cr-Commit-Position: refs/heads/master@{#323060}
54 files changed