mash: Cleanup ash shelf application menu code.

ash/common/shelf/shelf_application_menu_model.cc

Index: ash/common/shelf/shelf_application_menu_model.cc
diff --git a/ash/common/shelf/shelf_application_menu_model.cc b/ash/common/shelf/shelf_application_menu_model.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8695831c9d8ed5f6ed1e2129d2fb6d1a7bc81987
--- /dev/null
+++ b/ash/common/shelf/shelf_application_menu_model.cc
@@ -0,0 +1,72 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/common/shelf/shelf_application_menu_model.h"
+
+#include <stddef.h>
+
+#include <utility>
+
+#include "ash/public/cpp/shelf_application_menu_item.h"
+#include "base/metrics/histogram_macros.h"
+
+namespace {
+
+const int kInvalidCommandId = std::numeric_limits<int>::max();

[James Cook, 2017/02/06 17:30:21]

nit: #include <limits>

or use -1

[msw, 2017/02/07 09:12:00]

I included <limits>, negative values sadly doesn't work for SimpleMenuModel
non-separator command ids:
https://cs.chromium.org/chromium/src/ui/base/models/simple_menu_model.cc?l=455

[James Cook, 2017/02/07 16:32:24]

Acknowledged.

+
+const char kNumItemsEnabledHistogramName[] =
+    "Ash.Shelf.Menu.NumItemsEnabledUponSelection";

[James Cook, 2017/02/06 17:30:21]

I would just inline these histogram names below.

[msw, 2017/02/07 09:12:00]

Done.

+
+const char kSelectedMenuItemIndexHistogramName[] =
+    "Ash.Shelf.Menu.SelectedMenuItemIndex";
+
+}  // namespace
+
+namespace ash {
+
+ShelfApplicationMenuModel::ShelfApplicationMenuModel(
+    const base::string16& title,
+    ShelfApplicationMenuItems items)
+    : ui::SimpleMenuModel(this), items_(std::move(items)) {
+  AddSeparator(ui::SPACING_SEPARATOR);

[James Cook, 2017/02/06 17:30:21]

Do we want this if items_ is empty? In the old code it looks like
launcher_items_ could be empty. If that's no longer true,
DCHECK(!items_.empty());

[msw, 2017/02/07 09:12:00]

Hmm, there are tests for application menus without any items that I have
persisted, but the production code doesn't allow that to occur. I think we would
still want the title in that case, but it doesn't really seem to matter; I just
had to make sure that we don't add the last spacing separator (line 44) if there
are no items, otherwise the underlying menu code DCHECKS:
https://cs.chromium.org/chromium/src/ui/base/models/simple_menu_model.cc?l=134
Let me know if you want the behavior or testing changed here.

[James Cook, 2017/02/07 16:32:24]

I would just add a comment somewhere in here that items_ can be empty in tests,
maybe above line 43 with what you just explained to me.

[msw, 2017/02/07 18:19:15]

Done.

+  AddItem(kInvalidCommandId, title);
+  AddSeparator(ui::SPACING_SEPARATOR);
+
+  for (size_t i = 0; i < items_.size(); i++) {
+    ShelfApplicationMenuItem* item = items_[i].get();
+    AddItem(i, item->title());
+    if (!item->icon().IsEmpty())
+      SetIcon(GetIndexOfCommandId(i), item->icon());
+  }
+
+  if (!items_.empty())
+    AddSeparator(ui::SPACING_SEPARATOR);
+}
+
+ShelfApplicationMenuModel::~ShelfApplicationMenuModel() {}
+
+bool ShelfApplicationMenuModel::IsCommandIdChecked(int command_id) const {
+  return false;
+}
+
+bool ShelfApplicationMenuModel::IsCommandIdEnabled(int command_id) const {
+  return command_id >= 0 && static_cast<size_t>(command_id) < items_.size();

[James Cook, 2017/02/06 17:30:21]

optional fyi: size_t{foo} or int{bar} is acceptable style for numeric
conversions these days.

[msw, 2017/02/07 09:12:00]

Interesting, but I don't see any uses of that casting style with size_t in
codesearch (but do see uses with int). I think I'll leave this as-is for now.

+}
+
+void ShelfApplicationMenuModel::ExecuteCommand(int command_id,
+                                               int event_flags) {
+  DCHECK(IsCommandIdEnabled(command_id));
+  items_[command_id]->Execute(event_flags);
+  RecordMenuItemSelectedMetrics(command_id, items_.size());
+}
+
+void ShelfApplicationMenuModel::RecordMenuItemSelectedMetrics(
+    int command_id,
+    int num_menu_items_enabled) {
+  UMA_HISTOGRAM_COUNTS_100(kSelectedMenuItemIndexHistogramName, command_id);
+  UMA_HISTOGRAM_COUNTS_100(kNumItemsEnabledHistogramName,
+                           num_menu_items_enabled);
+}
+
+}  // namespace ash