Mus: Introduce DisplayCompositorClient mojo interface

cc/ipc/display_compositor.mojom

Index: cc/ipc/display_compositor.mojom
diff --git a/cc/ipc/display_compositor.mojom b/cc/ipc/display_compositor.mojom
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index 0000000000000000000000000000000000000000..c3ae783e6def4e62ec85589f59d0fd022b7503e4
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+// 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 cc.mojom;
+
+import "cc/ipc/surface_id.mojom";
+import "ui/gfx/geometry/mojo/geometry.mojom";
+
+// The DisplayCompositorClient interface is implemented by the Display
+// Compositor Host, a stable, and privileged peer service to the display
+// compositor. The display compositor host is either the browser process in
+// Chrome or the window server process.
+interface DisplayCompositorClient {
+  // Called by the display compositor immediately upon receiving a
+  // CompositorFrame with a new SurfaceId for the first time.
+  OnSurfaceCreated(cc.mojom.SurfaceId surface_id,
+                   gfx.mojom.Size frame_size,
+                   float device_scale_factor);
+};