Enable native custom elements for Pica benchmark

tools/perf/benchmarks/pica.py

Index: tools/perf/benchmarks/pica.py
diff --git a/tools/perf/benchmarks/pica.py b/tools/perf/benchmarks/pica.py
index 01920bdcda8511a32f6dae02f9b7b98b01602c9a..912252f577d1a39e6cd8519216a098d1aeef2de3 100644
--- a/tools/perf/benchmarks/pica.py
+++ b/tools/perf/benchmarks/pica.py
@@ -6,6 +6,10 @@ from telemetry import test
 from telemetry.page import page_measurement
 
 class PicaMeasurement(page_measurement.PageMeasurement):
+  def CustomizeBrowserOptions(self, options):
+    # Needed for native custom elements (document.register)
+    options.AppendExtraBrowserArg('--enable-experimental-web-platform-features')
+
   def MeasurePage(self, _, tab, results):
     result = int(tab.EvaluateJavaScript('__pica_load_time'))
     results.Add('Total', 'ms', result)