tools/perf WebRtc entries cleanup and grouping

Webrtc perf webrtc_cases are all grouped as one, whereas they
belong to at least four categories: simple GetUserMedia(),
PeerConnection, DataChannel and Audio. This CL separates this
bulk into four PageSets.

VGA versions are removed in favour of 720p, and regrouped.

With this, Webrtc rendering smoothness is just a flavour of the
Peerconnection one with some specific collected metrics, so it's
consolidated as another benchmark with the PeerConnection story.
Associated files are removed.

Relevant benchmarks read:
$ tools/perf/record_wpr --list-benchmarks
...
webrtc_audio                                                 Measures WebRtc Audio capture and local playback
webrtc_data_channel                                          Measures WebRtc DataChannel loopback
webrtc_getusermedia                                          Measures WebRtc GetUserMedia for video capture and local playback
webrtc_peer_connection                                       Measures WebRtc Peerconnection for remote video communication
webrtc_rendering                                             Specific time measurements (e.g. fps, smoothness) for WebRtc rendering.

and stories:

$ tools/perf/record_wpr --list-stories
...
webrtc_audio_page_set                              WebRTC tests for Real-time audio capture communication.
webrtc_datachannel_page_set                        WebRTC tests for Real-time communication via the data channel.
webrtc_getusermedia_page_set                       WebRTC tests for local getUserMedia: video capture and playback.
webrtc_peerconnection_page_set                     WebRTC tests for Real-time video communication.

BUG= 566244

*** Perf sheriffs ***
This CL changes the current structure of the webrtc
perf tests, that used to be, benchmarks:
web_rtc
web_rtcrendering

and stories:
webrtc_cases_page_set
webrtc_rendering_page_set

CQ_EXTRA_TRYBOTS=tryserver.chromium.perf:linux_perf_bisect;tryserver.chromium.perf:mac_10_10_perf_bisect;tryserver.chromium.perf:win_perf_bisect;tryserver.chromium.perf:android_nexus5_perf_bisect

Review URL: https://codereview.chromium.org/1497663002

Cr-Commit-Position: refs/heads/master@{#363694}
22 files changed