Convert startup_metric_utils to use mojo.

components/startup_metric_utils/common/startup_metric.mojom

Index: components/startup_metric_utils/common/startup_metric.mojom
diff --git a/components/startup_metric_utils/common/startup_metric.mojom b/components/startup_metric_utils/common/startup_metric.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..80161078ba809b47e6e0c63d173bc82bf910c1a9
--- /dev/null
+++ b/components/startup_metric_utils/common/startup_metric.mojom
@@ -0,0 +1,12 @@
+// Copyright 2016 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 startup_metric_utils.mojom;
+
+import "mojo/common/common_custom_types.mojom";
+
+interface StartupMetricHost {
+  RecordRendererMainEntryTime(
+      mojo.common.mojom.TimeTicks renderer_main_entry_time);

[dcheng, 2016/06/08 17:46:24]

General question: how can we make it easy for developers to find the mojo struct
that wraps the C++ type they want to use? If I wasn't looking for TimeTicks, I
don't think I'd know to look here.

[Sam McNally, 2016/06/09 00:20:53]

If everything is typemapped, something like
git grep 'base::TimeTicks' -- '*.typemap'
should find the typemap and the mojo struct name. The typemap will contain the
path to the mojom containing the type.

+};