Reland "Enable Perfetto by default for all telemetry tests"

This is a reland of 32c8ebbe

The last Perfetto roll in https://chromium-review.googlesource.com/c/chromium/src/+/1188362
includes a fix for the bug that caused the revert.

Original change's description:
> Enable Perfetto by default for all telemetry tests
>
> This will use Perfetto instead of TraceLog for all
> trace-based Telemetry tests running on Mac/Windows/Android.
>
> R=nednguyen@google.com
>
> Bug: 839084
> Cq-Include-Trybots: master.tryserver.chromium.perf:obbs_fyi
> Change-Id: I570060cd7f53ea0310f67370b4abec132c8a1a01
> Reviewed-on: https://chromium-review.googlesource.com/1176119
> Commit-Queue: oysteine <oysteine@chromium.org>
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Reviewed-by: Ned Nguyen <nednguyen@google.com>
> Cr-Commit-Position: refs/heads/master@{#585368}

TBR=nednguyen@google.com

Bug: 839084
Change-Id: Id416f7f81ae4f0056e80b678c32e608c2021d2ea
Cq-Include-Trybots: master.tryserver.chromium.perf:obbs_fyi
Reviewed-on: https://chromium-review.googlesource.com/1188752Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585934}

tools/perf/benchmarks/loading.py

@@ -18,11 +18,6 @@ class _LoadingBase(perf_benchmark.PerfBenchmark):
 
   options = {'pageset_repeat': 2}
 
-  def SetExtraBrowserOptions(self, options):
-    options.AppendExtraBrowserArgs([
-        '--enable-features=TracingPerfettoBackend',
-    ])
-
   def CreateCoreTimelineBasedMeasurementOptions(self):
     tbm_options = timeline_based_measurement.Options()
     loading_metrics_category.AugmentOptionsForLoadingMetrics(tbm_options)

tools/perf/core/perf_benchmark.py

@@ -104,6 +104,12 @@ class PerfBenchmark(benchmark.Benchmark):
     # with the test results.
     options.AppendExtraBrowserArgs(
         '--disable-gpu-process-for-dx12-vulkan-info-collection')
+
+    # Switch Chrome to use Perfetto instead of TraceLog as the tracing backend,
+    # needed until the feature gets turned on by default everywhere.
+    if options.browser_type != 'reference':
+      options.AppendExtraBrowserArgs(
+          '--enable-features=TracingPerfettoBackend')
     self.SetExtraBrowserOptions(options)
 
   @staticmethod