GMC: Make the GMC dialog scrollable

This CL modifies the MediaNotificationListView to be a ScrollView so
that the Global Media Controls dialog becomes scrollable when there are
too many sessions to fit comfortably.

Bug: 991370
Change-Id: Id5e9b92e455e4298dfcb7fd409b096f348bff232
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1745389Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685404}

chrome/browser/ui/views/global_media_controls/media_notification_list_view.cc

@@ -7,9 +7,17 @@
 #include "chrome/browser/ui/views/global_media_controls/media_notification_container_impl.h"
 #include "ui/views/layout/box_layout.h"
 
+namespace {
+
+constexpr int kMediaListMaxHeight = 478;
+
+}  // anonymous namespace
+
 MediaNotificationListView::MediaNotificationListView() {
-  SetLayoutManager(std::make_unique<views::BoxLayout>(
+  SetContents(std::make_unique<views::View>());
+  contents()->SetLayoutManager(std::make_unique<views::BoxLayout>(
       views::BoxLayout::Orientation::kVertical));
+  ClipHeightTo(0, kMediaListMaxHeight);
 }
 
 MediaNotificationListView::~MediaNotificationListView() = default;
@@ -20,7 +28,9 @@ void MediaNotificationListView::ShowNotification(
   DCHECK(!base::Contains(notifications_, id));
   DCHECK_NE(nullptr, notification.get());
 
-  notifications_[id] = AddChildView(std::move(notification));
+  notifications_[id] = contents()->AddChildView(std::move(notification));
+
+  contents()->InvalidateLayout();
   PreferredSizeChanged();
 }
 
@@ -28,7 +38,9 @@ void MediaNotificationListView::HideNotification(const std::string& id) {
   if (!base::Contains(notifications_, id))
     return;
 
-  RemoveChildView(notifications_[id]);
+  contents()->RemoveChildView(notifications_[id]);
   notifications_.erase(id);
+
+  contents()->InvalidateLayout();
   PreferredSizeChanged();
 }

chrome/browser/ui/views/global_media_controls/media_notification_list_view.h

@@ -8,13 +8,13 @@
 #include <map>
 #include <memory>
 
-#include "ui/views/view.h"
+#include "ui/views/controls/scroll_view.h"
 
 class MediaNotificationContainerImpl;
 
 // MediaNotificationListView is a container that holds a list of active media
 // sessions.
-class MediaNotificationListView : public views::View {
+class MediaNotificationListView : public views::ScrollView {
  public:
   MediaNotificationListView();
   ~MediaNotificationListView() override;