GMC: Reland 'Replace is_controllable DCHECK with if condition'

This CL relands a fix for a broken DCHECK in the
MediaToolbarButtonController. This fix was accidentally removed by a
bad rebase in a different CL.

Bug: 973486
Change-Id: Idb8cb0a8ceb251c82a81203ac2ef37ebc90fbf50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1695928Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676176}

chrome/browser/ui/global_media_controls/media_toolbar_button_controller.cc

@@ -39,11 +39,6 @@ MediaToolbarButtonController::~MediaToolbarButtonController() = default;
 
 void MediaToolbarButtonController::MediaSessionInfoChanged(
     media_session::mojom::MediaSessionInfoPtr session_info) {
-  if (session_info) {
-    // We only want to show if there's a controllable media session. However, as
-    // a MediaControllerObserver we should only receive a
-    // |MediaSessionInfoChanged()| call for a controllable session.
-    DCHECK(session_info->is_controllable);
+  if (session_info && session_info->is_controllable)
     delegate_->Show();
-  }
 }