mac: Revert to simplest undocked-only devtools.

This makes porting Chrome's devtools easier.
Place DevTools WebContents underneath inspected WebContents.

This commit has this strategy implemented on Mac.

See https://code.google.com/p/chromium/issues/detail?id=318751.
mac: Make focus back to browser window when devtools is closed.
No need to remember dock state.

All devtools states are remembered by devtools itself now.
Fix cpplint warning.
Aura has replaced GTK+ in Linux.
Remove devtools view on Linux.

GTK+ has been replaced, we need to rewrite the whole thing.
Define TOOLKIT_VIEWS for Linux.
Make BrowserMainParts's overrides available on all platforms.
Initialize Linux UI.
Link with chromiumviews on Linux and Windows.

Without using chromiumviews it would be quite hard to setup a fully working
environment with Aura on Linux now.
Ignore *_views files on mac.
Add ViewsDelegate, required when using views::Widget on aura.
Initialize screen for aura.
Allow override BrowserMainParts::InitProxyResolverV8.
Initialize aura environment.
views: Use chromium's custom frame view.
views: Initial docked devtools implementation.
views: Implement undocked devtools.
views: Remember bounds of devtools window.