1 files changed, 55 insertions, 0 deletions
diff --git a/layout/base/nsRefreshObservers.cpp b/layout/base/nsRefreshObservers.cpp
new file mode 100644
index 0000000000..44f797c0f1
--- /dev/null
+++ b/layout/base/nsRefreshObservers.cpp
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsRefreshObservers.h"
+#include "nsPresContext.h"
+#include "mozilla/Likely.h"
+
+namespace mozilla {
+
+ManagedPostRefreshObserver::ManagedPostRefreshObserver(nsPresContext* aPc,
+                                                       Action&& aAction)
+    : mPresContext(aPc), mAction(std::move(aAction)) {}
+
+ManagedPostRefreshObserver::ManagedPostRefreshObserver(nsPresContext* aPc)
+    : mPresContext(aPc) {
+  MOZ_ASSERT(mPresContext, "Can't observe without a nsPresContext");
+}
+
+ManagedPostRefreshObserver::~ManagedPostRefreshObserver() = default;
+
+void ManagedPostRefreshObserver::Cancel() {
+  // Caller holds a strong reference, so no need to reference stuff from here.
+  if (mAction) {
+    mAction(true);
+  }
+  mAction = nullptr;
+  mPresContext = nullptr;
+}
+
+void ManagedPostRefreshObserver::DidRefresh() {
+  if (MOZ_UNLIKELY(!mAction)) {
+    return;
+  }
+
+  RefPtr<ManagedPostRefreshObserver> thisObject = this;
+  auto action = std::move(mAction);
+  Unregister unregister = action(false);
+
+  if (unregister == Unregister::Yes) {
+    if (RefPtr<nsPresContext> pc = std::move(mPresContext)) {
+      // We have to null-check mPresContext here because in theory, mAction
+      // could've ended up in `Cancel` being called, which would clear
+      // mPresContext. In that case, we're already unregistered so no need to
+      // do anything.
+      pc->UnregisterManagedPostRefreshObserver(this);
+    }
+  } else {
+    mAction = std::move(action);
+  }
+}
+
+}  // namespace mozilla