Convert PowerSaveBlockResourceThrottle to be client of WakeLock mojo service.

Wake Lock is a Mojo interface that wraps PowerSaveBlocker. As part of the
creation of standalone Device Service, all browser-side clients of
PowerSaveBlocker should be converted to be clients of the Wake Lock Mojo
interface instead.

BUG=689410
TBR=jam@chromium.org, for mechanical changes to //content/browser/BUILD.gn

Review-Url: https://codereview.chromium.org/2893873002
Cr-Commit-Position: refs/heads/master@{#473076}
7 files changed