DevTools: expose Tracing agent to regular IPC clients
This exposes DevToolsTracingHandler using overrides in
RenderViewDevToolsAgentHost, so it can be used by regular
IPC DevTools front-ends, not just by HTTP clients.
Related blink change: https://codereview.chromium.org/
19005008/
R=pfeldman@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=212343
Review URL: https://codereview.chromium.org/
18748003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@212563 0039d316-1c4b-4281-b951-d872f2087c98