Turn off web security for devtools.
Upgrade libchromiumcontent to loose iframe sandbox.
Add chrome-extension protocol for loading devtools extensions.
Make "chrome-extension" a standard scheme.

If we do not do so, urls like "chrome-extension://extension-1" will
never get a hostname.
Don't use pure number as host name.

Numbers would be treated as IP addresses.
Ignore requests to other hosts.
Fix cpplint warnings.
Add support for chrome.extension API in devtools extension.
Add "dev-tools-opened" and "dev-tools-closed" events.
Remember loaded extensions.
dev-tools => devtools.
docs: Add docs on how to use chrome devtools extension.
Merge pull request #610 from atom/devtools-extension

Add support for chrome devtools extension