AppCache: Use BrowserInterfaceBrokerProxy for frames

This CL makes AppCache for frames use new BrowserInterfaceBrokerProxy mechanism
instead of DocumentInterfaceBroker.

Before this CL, AppCache used DocumentInterfaceBroker for frames, and
BrowserInterfaceBrokerProxy for workers. That complicated the code. After this
CL, both frames and workers use the same BrowserInterfaceBrokerProxy mechanism.

Relevant CL for AppCache for workers: https://crrev.com/c/1746128

Bug: 936482
Change-Id: I6f30ddec6d2055c9e4748c42a41c031f6c220b82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1758038
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689172}
17 files changed