Revert of DevTools: use explicit IPC messages for enabling/disabling tracing instead of intercepting protocol…

Revert of DevTools: use explicit IPC messages for enabling/disabling tracing instead of intercepting protocol… (patchset #3 of https://codereview.chromium.org/511873002/)

Reason for revert:
Creates timeout failures on a lot of inspector/ tests in Blink:
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20%28deps%29/builds/33453/steps/webkit_tests/logs/stdio

Original issue's description:
> DevTools: use explicit IPC messages for enabling/disabling tracing instead of intercepting protocol events
> 
> Added IPC plumbing that allows InspectorTracingAgent to enable/disable  browser-wide tracing. It was implemented by intercepting Tracing.started/Tracing.stopped events in the browser. Tracing.stopped event in the DevTools protocol was used by the renderer to notify the browser that it should stop trace event recording and it didn't make much sense for the client as there is already Tracing.tracingComplete event in the protocol.
> 
> BUG=398787
> 
> Committed: https://chromium.googlesource.com/chromium/src/+/a449adae35631e4791547bd0b14403d1766f9ddf

TBR=dcheng@chromium.org,caseq@chromium.org,loislo@chromium.org,vsevik@chromium.org,yurys@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=398787
Committed: https://crrev.com/cbe4516d6cdfa0eef5cff4822190254fd51dac1f
Cr-Commit-Position: refs/heads/master@{#292390}

[mlamouri (slow - plz ping), 2014-08-28 15:40:53]

Created Revert of DevTools: use explicit IPC messages for enabling/disabling
tracing instead of intercepting protocol…