[tools/perf] Add CompositorLatency.TotalLatency to benchmark report.

This CL adds CompositorLatency.TotalLatency to replace the pipeline:*
breakdowns that are to be removed in the benchmark report.

Bug: 1078160

Change-Id: I22241a5903d3b122c3e92cc80a1a019e697444e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2211918Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Mingjing Zhang <mjzhang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789359}

tools/perf/benchmarks/rendering.py

@@ -15,6 +15,7 @@ from telemetry.web_perf import timeline_based_measurement
 
 RENDERING_BENCHMARK_UMA = [
     'Compositing.Display.DrawToSwapUs',
+    'CompositorLatency.TotalLatency',
     'Event.Latency.ScrollBegin.Touch.TimeToScrollUpdateSwapBegin4',
     'Event.Latency.ScrollUpdate.Touch.TimeToScrollUpdateSwapBegin4',
     'Event.Latency.ScrollBegin.Wheel.TimeToScrollUpdateSwapBegin4',