Enable test PointerLockBrowserTest.PointerLockEventRouting

The tests in pointer_lock_browsertest.cc were flaky for 3 reasons:
- requestPointerLock being asynchronous
- mouse events being asynchronous
- native mouse events interfering with tests during execution
All the above were addressed in prior CLs.

Bug: 766450
Change-Id: I473623338fee3277cb905b17151f80a6468ebb57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2213107Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772367}

content/browser/pointer_lock_browsertest.cc

@@ -281,9 +281,7 @@ IN_PROC_BROWSER_TEST_F(PointerLockBrowserTest,
                        grand_child, EXECUTE_SCRIPT_NO_USER_GESTURE));
 }
 
-// Flaky test crbug.com/1077306
-IN_PROC_BROWSER_TEST_F(PointerLockBrowserTest,
-                       DISABLED_PointerLockEventRouting) {
+IN_PROC_BROWSER_TEST_F(PointerLockBrowserTest, PointerLockEventRouting) {
   GURL main_url(embedded_test_server()->GetURL(
       "a.com", "/cross_site_iframe_factory.html?a(b)"));
   EXPECT_TRUE(NavigateToURL(shell(), main_url));