Make AppWindowWaiter a common test support

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 068d93510e909d92603957e37d538dab243190f6..c1568919f8cd7085967a88381cfdf6141387ee60 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -187,6 +187,7 @@ static_library("test_support") {
 
   if (enable_extensions) {
     public_deps += [
+      "//apps:test_support",
       "//chrome/common/extensions/api",
       "//extensions:test_support",
     ]
@@ -248,6 +249,7 @@ static_library("test_support") {
 
   if (enable_extensions) {
     public_deps += [
+      "//apps:test_support",
       "//chrome/common/extensions/api",
       "//extensions:test_support",
     ]
@@ -2260,8 +2262,6 @@ test("browser_tests") {
         "../browser/chromeos/login/supervised/supervised_user_password_browsertest.cc",
         "../browser/chromeos/login/supervised/supervised_user_test_base.cc",
         "../browser/chromeos/login/supervised/supervised_user_test_base.h",
-        "../browser/chromeos/login/test/app_window_waiter.cc",
-        "../browser/chromeos/login/test/app_window_waiter.h",
         "../browser/chromeos/login/test/https_forwarder.cc",
         "../browser/chromeos/login/test/https_forwarder.h",
         "../browser/chromeos/login/test/oobe_base_test.cc",