Enable test CloseWindowFromWebAPIWhilePlaying

The Linux failures were due to https://crbug.com/1035382, which is now
fixed.

Thw Windows failures also seem to have been an unrelated issue that
affected hundreds of other tests in the same testrun:

[6532:7132:0731/151510.560:FATAL:service_process_host_impl.cc(57)] Check failed: iter != processes_.end().

Bug: 1001538
Change-Id: Ia87c54b7f71fd102cf49551db43541d74066846a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2513654
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823909}

chrome/browser/picture_in_picture/picture_in_picture_window_controller_browsertest.cc

@@ -622,9 +622,8 @@ IN_PROC_BROWSER_TEST_F(PictureInPictureWindowControllerBrowserTest,
 
 // Tests that when closing a Picture-in-Picture window from the Web API, the
 // video element is not paused.
-// Flaky on Linux and Windows: http://crbug.com/1001538
 IN_PROC_BROWSER_TEST_F(PictureInPictureWindowControllerBrowserTest,
-                       DISABLED_CloseWindowFromWebAPIWhilePlaying) {
+                       CloseWindowFromWebAPIWhilePlaying) {
   GURL test_page_url = ui_test_utils::GetTestUrl(
       base::FilePath(base::FilePath::kCurrentDirectory),
       base::FilePath(kPictureInPictureWindowSizePage));