telemetry: Disable top sites in thread_times benchmarks.

tools/perf/benchmarks/silk_flags.py

Index: tools/perf/benchmarks/silk_flags.py
diff --git a/tools/perf/benchmarks/silk_flags.py b/tools/perf/benchmarks/silk_flags.py
index 4b27dfdf03ea96e1887c3b6598db80353388ddac..080ed694370ed5b1bd24f36e700bc37dcae3f670 100644
--- a/tools/perf/benchmarks/silk_flags.py
+++ b/tools/perf/benchmarks/silk_flags.py
@@ -18,3 +18,8 @@ def CustomizeBrowserOptionsForGpuRasterization(options):
 def CustomizeBrowserOptionsForSyncScrolling(options):
   """Enables flags needed for synchronous (main thread) scrolling."""
   options.AppendExtraBrowserArgs('--disable-threaded-scrolling')
+
+def CustomizeBrowserOptionsForThreadTimes(options):
+  """Disables options known to cause noise in thread times"""
+  # Remove once crbug.com/621128 is fixed.
+  options.AppendExtraBrowserArgs('--disable-top-sites')