mac: ensure ui::Compositor exists for visible RWHVs

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index a59f6e4fcbc12dcad0ab73f6daa05b7a40838b4d..61f8529a9032fe331657ae13dd714620b76ff64c 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -197,6 +197,10 @@ static_library("test_support") {
   if (v8_use_external_startup_data) {
     deps += [ "//gin:gin" ]
   }
+
+  if (is_mac) {
+    deps += [ "//ui/accelerated_widget_mac" ]
+  }
 }
 
 # browsertest_support can be used by targets that run content_shell based
@@ -792,6 +796,7 @@ test("content_unittests") {
     deps += [
       "//third_party/mozilla",
       "//third_party/ocmock",
+      "//ui/accelerated_widget_mac",
     ]
   }
   if (is_chromeos) {