Reorganizes Chromecast code to better reflect functional dependencies.

Reorganizes Chromecast code to better reflect functional dependencies.

Motivation:
* chromecast/service/ directory had interplay with chromecast/shell/browser
  code, since the service is all run in the browser process and mildly
  coupled (involves starting WebContents instances, etc,). Made more sense
  for chromecast/service to live in chromecast/shell/browser.
* chromecast/shell/ directory is needless hierarchy, since the entire
  chromecast/ directory represents the Chromecast content-embedder.

Highlights:
* chromecast/shell/{app,browser,common,renderer} --> chromecast/*
* chromecast/shell/browser/resources --> chromecast/app/resources
* chromecast/shell/settings --> chromecast/app/resources
* chromecast/shell/android --> chromecast/browser/android
* chromecast/metrics --> chromecast/browser/metrics
* chromecast/service --> chromecast/browser/service

R=lcwu@chromium.org,gusfernandez@chromium.org,byungchul@chromium.org
TBR=xhwang@chromium.org,asvitkine@chromium.org,thestig@chromium.org,jam@chromium.org,yfriedman@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/638803002

Cr-Commit-Position: refs/heads/master@{#299385}