DevTools: Don't use debuggerId/processId getters on WebDevToolsAgentClient anymore.

We don't need to call methods on embedder, since we have all the information needed in blink.

R=pfeldman-OOO, yurys

Review URL: https://codereview.chromium.org/511763002

git-svn-id: svn://svn.chromium.org/blink/trunk@181040 bbb929c8-8fbe-4397-9dbb-9b2b20218538