Adds a mock for component_updater::ComponentUpdateService

components/component_updater/BUILD.gn

Index: components/component_updater/BUILD.gn
diff --git a/components/component_updater/BUILD.gn b/components/component_updater/BUILD.gn
index 1f9cfb4adf8449f866e614147ae82dce47cb5daa..45cbc32891522f445986523afb68e637cbdf2ade 100644
--- a/components/component_updater/BUILD.gn
+++ b/components/component_updater/BUILD.gn
@@ -32,6 +32,20 @@ source_set("component_updater") {
   ]
 }
 
+source_set("test_support") {
+  testonly = true
+  sources = [
+    "mock_component_updater_service.cc",
+    "mock_component_updater_service.h",
+  ]
+
+  public_deps = [
+    ":component_updater",
+    "//base",
+    "//testing/gmock",
+  ]
+}
+
 source_set("unit_tests") {
   testonly = true
   sources = [