Re-reland: Add MemoryCoordinator

components/memory_coordinator/child/BUILD.gn

 # 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.
 
 source_set("child") {
   sources = [
     "child_memory_coordinator_impl.cc",
     "child_memory_coordinator_impl.h",
   ]
 
   deps = [
     "//base",
+    "//components/memory_coordinator/public/interfaces",
+    "//services/shell/public/cpp",
+  ]
+
+  public_deps = [
     "//components/memory_coordinator/common",
-    "//components/memory_coordinator/public/interfaces",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
 
   sources = [
     "child_memory_coordinator_impl_unittest.cc",
   ]
 
   deps = [
     ":child",
     "//mojo/common",
     "//testing/gtest",
   ]
 }