Enable PointerLockBrowserTest.PointerLockWheelEventRouting

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: I08ba7c5f34d57a92e24480934cb6d2fc731fd6f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2213110Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771923}

content/browser/pointer_lock_browsertest.cc

@@ -529,9 +529,7 @@ IN_PROC_BROWSER_TEST_F(PointerLockBrowserTest, PointerLockOopifCrashes) {
   }
 }
 
-// Flaky test https://crbug.com/766450
-IN_PROC_BROWSER_TEST_F(PointerLockBrowserTest,
-                       DISABLED_PointerLockWheelEventRouting) {
+IN_PROC_BROWSER_TEST_F(PointerLockBrowserTest, PointerLockWheelEventRouting) {
   GURL main_url(embedded_test_server()->GetURL(
       "a.com", "/cross_site_iframe_factory.html?a(b)"));
   EXPECT_TRUE(NavigateToURL(shell(), main_url));