Split ExtensionTestObserver and move to //extensions.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 227b8aa2d3cd3b5f444a0d5f291d03778d7173f3..98a256cc9670861369bfe8cb6f3a32274364ffd2 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -370,6 +370,8 @@ if (!is_android) {
       "../browser/extensions/api/extension_action/browser_action_interactive_test.cc",
       "../browser/extensions/api/omnibox/omnibox_api_interactive_test.cc",
       "../browser/extensions/browsertest_util.cc",
+      "../browser/extensions/chrome_extension_test_notification_observer.cc",
+      "../browser/extensions/chrome_extension_test_notification_observer.h",
       "../browser/extensions/clipboard_extension_apitest_chromeos.cc",
       "../browser/extensions/extension_apitest.cc",
       "../browser/extensions/extension_browsertest.cc",
@@ -378,7 +380,6 @@ if (!is_android) {
       "../browser/extensions/extension_fullscreen_apitest.cc",
       "../browser/extensions/extension_function_test_utils.cc",
       "../browser/extensions/extension_keybinding_apitest.cc",
-      "../browser/extensions/extension_test_notification_observer.cc",
       "../browser/extensions/updater/extension_cache_fake.cc",
       "../browser/extensions/updater/extension_cache_fake.h",
       "../browser/extensions/window_open_interactive_apitest.cc",
@@ -2037,14 +2038,14 @@ test("browser_tests") {
         "../browser/apps/app_browsertest_util.h",
         "../browser/extensions/browsertest_util.cc",
         "../browser/extensions/browsertest_util.h",
+        "../browser/extensions/chrome_extension_test_notification_observer.cc",
+        "../browser/extensions/chrome_extension_test_notification_observer.h",
         "../browser/extensions/extension_apitest.cc",
         "../browser/extensions/extension_apitest.h",
         "../browser/extensions/extension_browsertest.cc",
         "../browser/extensions/extension_browsertest.h",
         "../browser/extensions/extension_function_test_utils.cc",
         "../browser/extensions/extension_function_test_utils.h",
-        "../browser/extensions/extension_test_notification_observer.cc",
-        "../browser/extensions/extension_test_notification_observer.h",
         "../browser/extensions/updater/extension_cache_fake.cc",
         "../browser/extensions/updater/extension_cache_fake.h",
       ]
@@ -4913,9 +4914,10 @@ if (!is_android && !is_ios && !is_chromecast) {
       "../browser/extensions/api/cast_streaming/performance_test.cc",
       "../browser/extensions/api/tab_capture/tab_capture_performancetest.cc",
       "../browser/extensions/browsertest_util.cc",
+      "../browser/extensions/chrome_extension_test_notification_observer.cc",
+      "../browser/extensions/chrome_extension_test_notification_observer.h",
       "../browser/extensions/extension_apitest.cc",
       "../browser/extensions/extension_browsertest.cc",
-      "../browser/extensions/extension_test_notification_observer.cc",
       "../browser/extensions/updater/extension_cache_fake.cc",
       "../browser/extensions/updater/extension_cache_fake.h",
       "base/browser_perf_tests_main.cc",