Use ContextUtils in PhysicalWeb

The Physical Web code currently requires a lot of passing around
Contexts where not necessary because we just want the Application.
This change uses ContextUtils.getApplicationContext() when applicable.

BUG=624204

Review-Url: https://codereview.chromium.org/2108983002
Cr-Commit-Position: refs/heads/master@{#404238}
11 files changed