Multipaste: Call observer function when removing clipboard history item.

ClipboardHistory::Observer::OnClipboardHistoryItemRemoved was only
called when removing an item from the list after the maximum number of
items was reached. This change also calls the removed function when an
item is manually removed with the 'x' button in the context menu.

Bug: 1154811
Change-Id: I274beba20d1671e3e7aabdcf7c0b17d97c29d547
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2569854
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833560}

ash/clipboard/clipboard_history.cc

@@ -56,7 +56,10 @@ void ClipboardHistory::RemoveItemForId(const base::UnguessableToken& id) {
   if (iter == history_list_.cend())
     return;
 
+  auto removed = std::move(*iter);
   history_list_.erase(iter);
+  for (auto& observer : observers_)
+    observer.OnClipboardHistoryItemRemoved(removed);
 }
 
 void ClipboardHistory::OnClipboardDataChanged() {