[Picture-in-Picture] Add missing [NewObject] to methods in IDL.

Updated spec says IDL for requestPictureInPicture and
exitPictureInPicture should specify that a new object is returned.

https://github.com/WICG/picture-in-picture/pull/76

Bug: 806249
Change-Id: Iba50455ef30c97d87c3e22b9ac95bc4bc41d546d
Reviewed-on: https://chromium-review.googlesource.com/1122226Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#572257}

third_party/blink/renderer/modules/picture_in_picture/document_picture_in_picture.idl

@@ -11,7 +11,7 @@
 partial interface Document {
     [Measure] readonly attribute boolean pictureInPictureEnabled;
 
-    [CallWith=ScriptState, Measure] Promise<void> exitPictureInPicture();
+    [CallWith=ScriptState, Measure, NewObject] Promise<void> exitPictureInPicture();
 
     // TODO(crbug.com/656517): Define this attribute in DocumentOrShadowRoot.
     [Measure] readonly attribute HTMLVideoElement? pictureInPictureElement;

third_party/blink/renderer/modules/picture_in_picture/html_video_element_picture_in_picture.idl

@@ -8,7 +8,7 @@
     RuntimeEnabled=PictureInPictureAPI
 ]
 partial interface HTMLVideoElement {
-    [CallWith=ScriptState, Measure] Promise<PictureInPictureWindow> requestPictureInPicture();
+    [CallWith=ScriptState, Measure, NewObject] Promise<PictureInPictureWindow> requestPictureInPicture();
 
     attribute EventHandler onenterpictureinpicture;
     attribute EventHandler onleavepictureinpicture;