Add tooltips to GMC skip and seek controls

The |accessible_name| passed to
MediaNotificationViewImpl::CreateMediaButton is now used as the tooltip
text.

Bug: 1047294
Change-Id: Ie60dff78aed15159d83ac1d5aa5192d2cf539207
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250881
Commit-Queue: Noah Rose Ledesma <noahrose@google.com>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779523}

components/media_message_center/media_notification_view_impl.cc

@@ -554,6 +554,7 @@ void MediaNotificationViewImpl::CreateMediaButton(
   button->set_tag(static_cast<int>(action));
   button->SetPreferredSize(kMediaButtonSize);
   button->SetAccessibleName(accessible_name);
+  button->SetTooltipText(accessible_name);
   button->SetFocusBehavior(views::View::FocusBehavior::ALWAYS);
   button_row_->AddChildView(std::move(button));
 }

components/media_message_center/media_notification_view_impl.h

@@ -98,7 +98,8 @@ class COMPONENT_EXPORT(MEDIA_MESSAGE_CENTER) MediaNotificationViewImpl
 
   // Creates an image button with an icon that matches |action| and adds it
   // to |button_row_|. When clicked it will trigger |action| on the session.
-  // |accessible_name| is the text used for screen readers.
+  // |accessible_name| is the text used for screen readers and the
+  // button's tooltip.
   void CreateMediaButton(media_session::mojom::MediaSessionAction action,
                          const base::string16& accessible_name);