Mus: Introduce DisplayCompositorClient mojo interface

cc/ipc/BUILD.gn

Index: cc/ipc/BUILD.gn
diff --git a/cc/ipc/BUILD.gn b/cc/ipc/BUILD.gn
index 53b3fec7e6dd908721f8e35e3e356cd2d78bd702..3e9b21aa9a623a705ceafe13cf7a145dca3cf0ad 100644
--- a/cc/ipc/BUILD.gn
+++ b/cc/ipc/BUILD.gn
@@ -57,7 +57,7 @@ mojom("interfaces") {
     "transferable_resource.mojom",
   ]
 
-  deps = [
+  public_deps = [
     "//gpu/ipc/common:interfaces",
     "//mojo/common:common_custom_types",
     "//skia/public/interfaces",
@@ -67,6 +67,18 @@ mojom("interfaces") {
   ]
 }
 
+# Interfaces between two privileged services.
+mojom("internal_interfaces") {
+  sources = [
+    "display_compositor.mojom",
+  ]
+
+  public_deps = [
+    ":interfaces",
+    "//ui/gfx/geometry/mojo",
+  ]
+}
+
 mojom("test_interfaces") {
   testonly = true
   sources = [