arc: enable Android tracing in verified-boot mode

components/arc/common/tracing.mojom

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Next MinVersion: 1
+// Next MinVersion: 2
 
 module arc.mojom;
 
 interface TracingInstance {
   // Queries available tracing categories in the container.
   QueryAvailableCategories@0() => (array<string> categories);
 
-  // Starts tracing in the container with the given categories.
-  StartTracing@1(array<string> categories) => (bool success);
+  // Starts tracing in the container with the given categories. A handle is
+  // passed to the client for sending trace events back to the host. The client
+  // should send trace event as a JSON object in each write.
+  StartTracing@1(array<string> categories,
+                 [MinVersion=1] handle? socket) => (bool success);
 
   // Stops tracing in the container.
   StopTracing@2() => (bool success);
 };