appcache: Move AppCacheNamespace from content/common to content/browser.

AppCacheNamespace is only used in AppCache's browser-side
implementation. Having it in content/common/appcache_interfaces.h is
misleading, as it suggests that the class is shared with the renderer.

Bug: 611938
Change-Id: Iffcb77f27408f133c97417663d48d244f2a672bd
Reviewed-on: https://chromium-review.googlesource.com/c/1429246
Auto-Submit: Victor Costan <pwnall@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625240}
8 files changed