[clock sync] Add the TELEMETRY clock domain to the controller's trace

telemetry/telemetry/internal/platform/tracing_controller_backend.py

Index: telemetry/telemetry/internal/platform/tracing_controller_backend.py
diff --git a/telemetry/telemetry/internal/platform/tracing_controller_backend.py b/telemetry/telemetry/internal/platform/tracing_controller_backend.py
index 09dab26f52a94d3742998974370e425f1652ee1e..a1b0e5e2ba778a2893e69c1e3a96c4068b13528e 100644
--- a/telemetry/telemetry/internal/platform/tracing_controller_backend.py
+++ b/telemetry/telemetry/internal/platform/tracing_controller_backend.py
@@ -238,7 +238,23 @@ class TracingControllerBackend(object):
     assert not trace_event.trace_is_enabled(), 'Stop tracing before collection.'
     with open(self._trace_log, 'r') as fp:
       data = ast.literal_eval(fp.read() + ']')
-    trace_data_builder.AddEventsTo(trace_data_module.TELEMETRY_PART, data)
+    trace_data_builder.SetTraceFor(trace_data_module.TELEMETRY_PART, {
+        "traceEvents": data,
+        "metadata": {
+            # TODO(charliea): For right now, we use "TELEMETRY" as the clock
+            # domain to guarantee that Telemetry is given its own clock
+            # domain. Telemetry isn't really a clock domain, though: it's a
+            # system that USES a clock domain like LINUX_CLOCK_MONOTONIC or
+            # WIN_QPC. However, there's a chance that a Telemetry controller
+            # running on Linux (using LINUX_CLOCK_MONOTONIC) is interacting with
+            # an Android phone (also using LINUX_CLOCK_MONOTONIC, but on a
+            # different machine). The current logic collapses clock domains
+            # based solely on the clock domain string, but we really should to
+            # collapse based on some (device ID, clock domain ID) tuple. Giving
+            # Telemetry its own clock domain is a work-around for this.
+            "clock-domain": "TELEMETRY"
+      }
+    })
     try:
       os.remove(self._trace_log)
       self._trace_log = None