tracing: Introduce mojo Interfaces

services/resource_coordinator/public/interfaces/tracing/tracing.mojom

Index: services/resource_coordinator/public/interfaces/tracing/tracing.mojom
diff --git a/services/resource_coordinator/public/interfaces/tracing/tracing.mojom b/services/resource_coordinator/public/interfaces/tracing/tracing.mojom
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+// 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.
+
+module resource_coordinator.tracing.mojom;
+
+import "mojo/common/time.mojom";
+import "mojo/common/values.mojom";
+
+// The JSON type of data coming from a tracing agents.
+//
+// - All agents with the same label should have the same type.
+// - There can be multiple agents with the same label, if their data type is
+//   ARRAY. Their data will be concatenated together and separated by commas.
+// - There can be only one agent with data type STRING.
+enum TraceDataType {
+  ARRAY,
+  STRING
+};
+
+// Tracing agents, like |chrome|, |etw|, |battor|, and |cros|, use this
+// interface to register themselves to the tracing service.
+interface Factory {
+  RegisterAgent(Agent agent, string name, string label, TraceDataType type,
+                bool supports_explicit_clock_sync_);
+};
+
+// There should be at most one implementation of this interface per process.
+// When the tracing service calls |StopAndFlush| on an agent, the agent begins
+// serializing data into the recorder that was given in the |StartTracing| call.
+// When finished, the agent should close the recorder connection to signal the
+// tracing service that no more data will be sent.
+interface Agent {
+  StartTracing(string categories, Recorder recorder);
+  StopAndFlush();
+  RequestClockSyncMarker() => (mojo.common.mojom.TimeTicks issue_ts,
+                               mojo.common.mojom.TimeTicks issue_end_ts);
+  RequestBufferStatus() => (uint32 capacity, uint32 count);
+};
+
+// An agent can make several calls to |AddChunk|. Chunks will be concatenated
+// with no separator (type STRING) or using comma as the separator (type ARRAY).
+// There should be only one agent of type STRING per agent label; otherwise
+// their trace data would be mixed up.
+interface Recorder {
+  AddChunk(string chunk);
+  AddMetadata(mojo.common.mojom.DictionaryValue metadata);
+};
+
+// A tracing controller uses this interface to coordinate trace data collection
+// from all registered agents. At any given time, there should be at most one
+// connected controller.
+interface Coordinator {
+  StartTracing(handle<data_pipe_producer> stream, string categories);
+  StopAndFlush();
+  IsTracing() => (bool is_tracing);
+  RequestBufferUsage() => (float percent_full, uint32 approximate_count);
+};