[DevTools] Add power profiling definition in devtools protocol.

This change add power domain in devtools protocol, with command start / stop,
and events dataAvailable.

BUG=337138

Review URL: https://codereview.chromium.org/165533004

git-svn-id: svn://svn.chromium.org/blink/trunk@167178 bbb929c8-8fbe-4397-9dbb-9b2b20218538