Pausable Object Cleanup - IDBRequest

IDBRequest doesn't need to be a pausable object since it doesn't use any
PausableObject behaviour and can just be a ContextLifecycleObserver.

BUG=907125

Change-Id: Ief75293c6bced70f781f0c716f1d121fe39f2e3b
Reviewed-on: https://chromium-review.googlesource.com/c/1387546
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618552}
3 files changed