[telemetry] Enable flow events by default.

tools/telemetry/telemetry/core/platform/profiler/trace_profiler.py

Index: tools/telemetry/telemetry/core/platform/profiler/trace_profiler.py
diff --git a/tools/telemetry/telemetry/core/platform/profiler/trace_profiler.py b/tools/telemetry/telemetry/core/platform/profiler/trace_profiler.py
index cbeb8b71b379401844f508bbbcff2ec2aee0f60a..58d8d4283a6207fb2a9399edad841fda0e4fd54b 100644
--- a/tools/telemetry/telemetry/core/platform/profiler/trace_profiler.py
+++ b/tools/telemetry/telemetry/core/platform/profiler/trace_profiler.py
@@ -14,7 +14,11 @@ class TraceProfiler(profiler.Profiler):
     super(TraceProfiler, self).__init__(
         browser_backend, platform_backend, output_path, state)
     assert self._browser_backend.supports_tracing
-    self._browser_backend.StartTracing(categories, timeout=10)
+    # We always want flow events when tracing via telemetry.
+    categories_with_flow = 'disabled-by-default-toplevel.flow'
+    if categories:
+      categories_with_flow = ',%s' % categories
+    self._browser_backend.StartTracing(categories_with_flow, timeout=10)
 
   @classmethod
   def name(cls):