Revert "Enable Perfetto by default for all telemetry tests"

This reverts commit 32c8ebbe.

Reason for revert: [sheriff] This might be a culprit for consistent
failures [4 out of the last 4 builds] of telemetry_perf_unittests
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29

Started at https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29/73930

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=oysteine@chromium.org,skyostil@chromium.org,nednguyen@google.com

Change-Id: I162f26045f454c23eae1b99af5b3168c7f7b9e44
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 839084
Cq-Include-Trybots: master.tryserver.chromium.perf:obbs_fyi
Reviewed-on: https://chromium-review.googlesource.com/1186301Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585423}

tools/perf/benchmarks/loading.py

@@ -18,6 +18,11 @@ 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

@@ -104,12 +104,6 @@ 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