Propagate fullscreen request type for OOPIF

Propagate the actual fullscreen request type to OOPIF fullscreen
ancestors so that they fire matching prefixed or unprefixed
fullscreen events.

(Previously, it was always using "unprefixed" for OOPIF.)

Change-Id: I04000d2190e06127329db1d91565914227aa9480
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2351000
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797833}

third_party/blink/renderer/core/frame/fullscreen_controller.cc

@@ -155,16 +155,11 @@ void FullscreenController::EnterFullscreen(LocalFrame& frame,
       fullscreen_options->display_id = options->screen()->DisplayId();
   }
 
-  // TODO(alexmos): currently, this assumes prefixed requests, but in the
-  // future, this should plumb in information about which request type
-  // (prefixed or unprefixed) to use for firing fullscreen events.
-  //
-  // This is basically implemented, but disabled for now since it's potentially
-  // an application-visible change in behavior. To enable, use the following:
-  //
-  //   fullscreen_options->is_prefixed =
-  //       request_type & FullscreenRequestType::kPrefixed;
-  fullscreen_options->is_prefixed = true;
+  // Propagate the type of fullscreen request (prefixed or unprefixed) to
+  // OOPIF ancestor frames so that they fire matching prefixed or unprefixed
+  // fullscreen events.
+  fullscreen_options->is_prefixed =
+      request_type & FullscreenRequestType::kPrefixed;
 
 #if DCHECK_IS_ON()
   DVLOG(2) << __func__ << ": request_type="