Move extension_test_message_listener to extensions.

This CL is part of the refactoring of webview into extensions/, and the webview test infrastructure depends heavily on this. Webview tests will be added to extensions soon.

BUG=352290

Review URL: https://codereview.chromium.org/584513003

Cr-Commit-Position: refs/heads/master@{#295665}
diff --git a/chrome/browser/extensions/shared_module_apitest.cc b/chrome/browser/extensions/shared_module_apitest.cc
index dc33302..71fcfbfd 100644
--- a/chrome/browser/extensions/shared_module_apitest.cc
+++ b/chrome/browser/extensions/shared_module_apitest.cc
@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/extension_apitest.h"
-#include "chrome/browser/extensions/extension_test_message_listener.h"
+#include "extensions/test/extension_test_message_listener.h"
 
 using extensions::Extension;