Always generate profile ids on the front-end

We used to extract id from heap snapshot but after this change all profiles will be assigned consecutive ids generated by the front-end.

BUG=324769
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/142473004

git-svn-id: svn://svn.chromium.org/blink/trunk@166197 bbb929c8-8fbe-4397-9dbb-9b2b20218538