Add support for multiple Timeline recordings.

We also don't explicitly add ResourceTimelineRecords anymore. These will be tracked automatically in a later patch.

https://bugs.webkit.org/show_bug.cgi?id=123366

Reviewed by Joseph Pecoraro.

* UserInterface/DashboardManager.js:
(WebInspector.DashboardManager.prototype._mainResourceDidChange): Check for currentRecording.
* UserInterface/InspectorFrontendAPI.js:
(InspectorFrontendAPI.isTimelineProfilingEnabled): Check for currentRecording.
* UserInterface/Main.html:
* UserInterface/TimelineManager.js:
(WebInspector.TimelineManager):
(WebInspector.TimelineManager.prototype.get currentRecording): Added.
(WebInspector.TimelineManager.prototype.startRecording): Make a new recording and push it onto the recording array.
Add the current recording to the event.
(WebInspector.TimelineManager.prototype.stopRecording): Add the current recording to the event.
(WebInspector.TimelineManager.prototype.eventRecorded.processRecord): Check for currentRecording. Add the markers
to the current recording.
(WebInspector.TimelineManager.prototype._addRecord): Add the record to the current recording.
(WebInspector.TimelineManager.prototype._startAutoRecording): Clean up. Don't add ResourceTimelineRecord. Clear recordings.
(WebInspector.TimelineManager.prototype._stopAutoRecordingSoon): Check for _currentRecording.
(WebInspector.TimelineManager.prototype._resetAutoRecordingDeadTimeTimeout): Ditto.
(WebInspector.TimelineManager.prototype._mainResourceDidChange): Don't add ResourceTimelineRecord anymore.
(WebInspector.TimelineManager.prototype._resourceWasAdded): Removed.
* UserInterface/TimelineRecording.js: Added.
(WebInspector.TimelineRecording): Added.
(WebInspector.TimelineRecording.prototype.addEventMarker): Added.
(WebInspector.TimelineRecording.prototype.addRecord): Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162400 268f45cc-cd09-0410-ab3c-d52691b4dbfc