Cleanup LayoutTests that define a function gc().

third_party/WebKit/LayoutTests/media/mediasession/mojo/callback-alive-after-gc.html

Index: third_party/WebKit/LayoutTests/media/mediasession/mojo/callback-alive-after-gc.html
diff --git a/third_party/WebKit/LayoutTests/media/mediasession/mojo/callback-alive-after-gc.html b/third_party/WebKit/LayoutTests/media/mediasession/mojo/callback-alive-after-gc.html
index cab68b4598d1171ebf459c9ce1a4840bcba44916..bfe2ab1efdbc465cddc465da3bd837abc2b88f00 100644
--- a/third_party/WebKit/LayoutTests/media/mediasession/mojo/callback-alive-after-gc.html
+++ b/third_party/WebKit/LayoutTests/media/mediasession/mojo/callback-alive-after-gc.html
@@ -3,22 +3,13 @@
 <script src="../../../resources/testharness.js"></script>
 <script src="../../../resources/testharnessreport.js"></script>
 <script src="../../../resources/mojo-helpers.js"></script>
+<script src="../../../resources/gc.js"></script>
 <script src="resources/mediasessionservice-mock.js"></script>
 <script src="resources/utils.js"></script>
 <script>
 
 var mock;
 
-function gc() {
-  if (window.GCController) {
-    GCController.collect();
-  } else {
-    for (var i = 0; i < 10000; ++i) {
-      ({ });
-    }
-  }
-}
-
 async_test(function(t) {
   mediaSessionServiceMock.then(m => {
     mock = m;