CPU profiler cleanup

Removed some front-end code that used only for instrumenting profiler.

Removed ProfileHeader.typeId and CPUProfileNode.numberOfCalls from the protocol. Made head and idleTime fields mandatory for CPUProfile.

BUG=None
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/21552002

git-svn-id: svn://svn.chromium.org/blink/trunk@155331 bbb929c8-8fbe-4397-9dbb-9b2b20218538