Make chrome inspector timeline backend use the new bufferEvents option.

The purpose if this is to reduce the overhead of timeline recording so that speed index might be run with page cyclers. 

It's been established that timeline events should be inaccessible by Telemetry measurements until recording is stopped, so it seems reasonable to switch to this mode for any timeline recording.

BUG=295334

Review URL: https://codereview.chromium.org/46503003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239393 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239393