Chromecast: removes devtools resources from bundle.

The devtools discovery page is rewritten/cleaned up to support two
optional paths for users:
1) Use the remote AppEngine debugger, which connects over WebSockets
   to the device. This triggers a security warning, so a help link
   is added for the user.
2) Provide a link to the Chrome native devtools UI for users.,,

Review URL:

Cr-Commit-Position: refs/heads/master@{#302013}
4 files changed