Add new metrics for ad_tagging.cluster_telemetry benchmark

Adds PageLoad.Cpu.TotalUsage and
PageLoad.PaintTiming.NavigationToFirstContentfulPaint, which are both
high-level metrics that allow us to track the impact of (ads and other)
scripts on page load performance.

Bug: 1036160
Change-Id: I530481cd5023d159624defb7e9ccf992945d0b24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1977957
Commit-Queue: Alex Turner <alexmt@chromium.org>
Reviewed-by: John Delaney <johnidel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728216}

tools/perf/contrib/cluster_telemetry/ad_tagging_ct.py

@@ -44,7 +44,9 @@ class AdTaggingClusterTelemetry(perf_benchmark.PerfBenchmark):
         'PageLoad.Clients.Ads.Cpu.AdFrames.Aggregate.TotalUsage',
         'PageLoad.Clients.Ads.Cpu.FullPage.TotalUsage',
         'PageLoad.Clients.Ads.Resources.Bytes.Ads2',
+        'PageLoad.Cpu.TotalUsage',
         'PageLoad.Experimental.Bytes.NetworkIncludingHeaders',
+        'PageLoad.PaintTiming.NavigationToFirstContentfulPaint',
     ]
     for histogram in uma_histograms:
       tbm_options.config.chrome_trace_config.EnableUMAHistograms(histogram)