Report Unique_frames_count from frame_analyzer using 'score' units.
Report Unique_frames_count from frame_analyzer using 'score' units.

With this change, an increase in Unique_frames_count will be marked
as an improvement (rather than a deterioration) in the Chrome Performance
Dashboard.

BUG=chromium:623521
R=phoglund@webrtc.org

Review-Url: https://codereview.webrtc.org/2142813002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#13444}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d658edeeedf1efd50a373f0ec90dfd54ce955527

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk