Add stats collection for telemetry startup.warm.blank_page test.

mojo/services/tracing/public/interfaces/tracing.mojom

Index: mojo/services/tracing/public/interfaces/tracing.mojom
diff --git a/mojo/services/tracing/public/interfaces/tracing.mojom b/mojo/services/tracing/public/interfaces/tracing.mojom
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+// Copyright 2014 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 tracing;
+
+// To participate in the tracing ecosystem, implement the TraceController
+// interface and connect to the tracing app. Then, when the controller's Start()
+// function is called collect tracing data and pass it back via the provided
+// TraceDataCollector interface up until Stop() is called.
+
+interface TraceController {
+  StartTracing(string categories, TraceDataCollector collector);
+  StopTracing();
+};
+
+interface TraceDataCollector {
+  DataCollected(string json);
+};
+
+interface TraceCoordinator {
+  // Request tracing data from all connected TraceControllers to stream to
+  // |stream|.
+  Start(handle<data_pipe_producer> stream, string categories);
+
+  // Stop tracing and flush results to file.
+  StopAndFlush();
+};
+
+// These times are used to determine startup performance metrics.
+// TODO(msw): Use TimeTicks to avoid system clock changes: crbug.com/521164
+struct StartupPerformanceTimes {
+  // TODO(msw): Rename to match "BrowserMainEntryTimeAbsolute" metric?
+  int64 shell_process_creation_time;
+  int64 browser_message_loop_start_time;
+  int64 browser_window_display_time;
+  int64 browser_open_tabs_time;
+  // TODO(msw): Rename to avoid "web contents"?
+  int64 first_web_contents_main_frame_load_time;
+  // TODO(msw): Rename to match "FirstWebContents.NonEmptyPaint" metric?
+  int64 first_visually_non_empty_layout_time;
+};
+
+// This interface accepts startup performance timing from a variety of sources.
+interface StartupPerformanceDataCollector {
+  // These setters may be called many times, only the first time is recorded.
+  SetShellProcessCreationTime(int64 time);
+  SetBrowserMessageLoopStartTime(int64 time);
+  SetBrowserWindowDisplayTime(int64 time);
+  SetBrowserOpenTabsTime(int64 time);
+  SetFirstWebContentsMainFrameLoadTime(int64 time);
+  SetFirstVisuallyNonEmptyLayoutTime(int64 time);
+
+  // Get the currently available startup performance times.
+  GetStartupPerformanceTimes() => (StartupPerformanceTimes times);
+};