[Picture-in-Picture] Resolve with current window if video is pipElement.

This make sures requestPictureInPicture is resolved with existing
Picture-in-Picture window when video is already pictureInPictureElement.

Bug: 806249
Change-Id: I16e3fc2e8e19c2b623e8d2518fe4672a2a16b756
Reviewed-on: https://chromium-review.googlesource.com/1101686
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567934}

third_party/WebKit/LayoutTests/external/wpt/picture-in-picture/picture-in-picture-window.html

@@ -34,6 +34,34 @@ promise_test(async t => {
 
 promise_test(async t => {
   const video = await loadVideo();
+
+  video.addEventListener('leavepictureinpicture', t.step_func_done(event => {
+    assert_unreached('leavepictureinpicture event should not fire.')
+  }));
+
+  let enterCounts = 0;
+  video.addEventListener('enterpictureinpicture', event => {
+    enterCounts++;
+  });
+
+  return requestPictureInPictureWithTrustedClick(video)
+  .then(pipWindow1 => {
+    pipWindow1.onresize = function foo() {};
+    return requestPictureInPictureWithTrustedClick(video)
+    .then(pipWindow2 => {
+      assert_equals(pipWindow1, pipWindow2);
+      assert_equals(pipWindow1.width, pipWindow2.width);
+      assert_equals(pipWindow1.height, pipWindow2.height);
+      assert_equals(pipWindow1.onresize, pipWindow2.onresize);
+      assert_equals(enterCounts, 1);
+    });
+  });
+}, 'Picture-in-Picture window is unchanged after entering ' +
+   'Picture-in-Picture for video already in Picture-in-Picture');
+
+promise_test(async t => {
+  const video = await loadVideo();
+
   return requestPictureInPictureWithTrustedClick(video)
   .then(pipWindow => {
     return document.exitPictureInPicture()

third_party/blink/renderer/modules/picture_in_picture/picture_in_picture_controller_impl.cc

@@ -82,9 +82,16 @@ PictureInPictureControllerImpl::IsElementAllowed(
 void PictureInPictureControllerImpl::EnterPictureInPicture(
     HTMLVideoElement* element,
     ScriptPromiseResolver* resolver) {
-  element->enterPictureInPicture(WTF::Bind(
-      &PictureInPictureControllerImpl::OnEnteredPictureInPicture,
-      WrapPersistent(this), WrapPersistent(element), WrapPersistent(resolver)));
+  if (picture_in_picture_element_ != element) {
+    element->enterPictureInPicture(
+        WTF::Bind(&PictureInPictureControllerImpl::OnEnteredPictureInPicture,
+                  WrapPersistent(this), WrapPersistent(element),
+                  WrapPersistent(resolver)));
+    return;
+  }
+
+  if (resolver)
+    resolver->Resolve(picture_in_picture_window_);
 }
 
 void PictureInPictureControllerImpl::OnEnteredPictureInPicture(