Add metrics to track buttons clicked in IME menu tray.

ash/common/system/chromeos/ime_menu/ime_menu_tray.cc

 // Copyright 2016 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/system/chromeos/ime_menu/ime_menu_tray.h"
 
 #include "ash/common/accessibility_delegate.h"
 #include "ash/common/ash_constants.h"
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shelf/wm_shelf.h"
 #include "ash/common/shelf/wm_shelf_util.h"
 #include "ash/common/system/chromeos/ime_menu/ime_list_view.h"
 #include "ash/common/system/tray/fixed_sized_scroll_view.h"
 #include "ash/common/system/tray/hover_highlight_view.h"
 #include "ash/common/system/tray/system_menu_button.h"
 #include "ash/common/system/tray/system_tray_controller.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "ash/common/system/tray/system_tray_notifier.h"
 #include "ash/common/system/tray/tray_constants.h"
 #include "ash/common/system/tray/tray_popup_item_style.h"
 #include "ash/common/system/tray/tray_popup_utils.h"
 #include "ash/common/system/tray/tray_utils.h"
 #include "ash/common/wm_lookup.h"
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/public/cpp/shell_window_ids.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "grit/ash_resources.h"
 #include "grit/ash_strings.h"
 #include "ui/base/ime/chromeos/input_method_manager.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/gfx/range/range.h"
 #include "ui/gfx/vector_icons_public.h"
 #include "ui/keyboard/keyboard_controller.h"
@@ skipping 156 matching lines @@
     if (sender == settings_button_) {
       ime_menu_tray_->HideImeMenuBubble();
       ShowIMESettings();
       return;
     }
 
     // The |keyset| will be used for drawing input view keyset in IME
     // extensions. InputMethodManager::ShowKeyboardWithKeyset() will deal with
     // the |keyset| string to generate the right input view url.
     std::string keyset;
-    if (sender == emoji_button_)
+    if (sender == emoji_button_) {
       keyset = "emoji";
-    else if (sender == voice_button_)
+      UMA_HISTOGRAM_COUNTS("InputMethod.ImeMenu.EmojiButton", 1);
+    } else if (sender == voice_button_) {
       keyset = "voice";
-    else if (sender == handwriting_button_)
+      UMA_HISTOGRAM_COUNTS("InputMethod.ImeMenu.VoiceButton", 1);
+    } else if (sender == handwriting_button_) {
       keyset = "hwt";
-    else
+      UMA_HISTOGRAM_COUNTS("InputMethod.ImeMenu.HandwritingButton", 1);

[Alexei Svitkine (slow), 2017/01/03 15:47:22]

UMA_HISTOGRAM_COUNTS allocates 50 buckets but you're only logging to bucket 1.
This is wasteful.

It would be more efficient to log an UMA_HISTOGRAM_BOOLEAN.

However, given you have 3 things that are related, you would be better served
making this an enum histogram, with the different cases as different enum
entries.

If you do that, suggest making a helper function to log the enum histogram so
that you don't repeat the macro - as each macro expands to a bunch of code and
thus multiple macro statements bloat the binary.

[Azure Wei, 2017/01/04 14:02:41]

Thanks. I've updated these with enum histogram and added a helper method
RecordButtonsClicked(). Please take another look. Thanks!

+    } else {
       NOTREACHED();
+    }
 
     ime_menu_tray_->ShowKeyboardWithKeyset(keyset);
   }
 
   // ViewClickListener:
   void OnViewClicked(views::View* sender) override {
     if (one_settings_button_view_ && sender == one_settings_button_view_) {
       ime_menu_tray_->HideImeMenuBubble();
       ShowIMESettings();
     }
@@ skipping 364 matching lines @@
   WmShell::Get()->system_tray_delegate()->GetCurrentIME(&current_ime_);
 
   // Updates the tray label based on the current input method.
   if (current_ime_.third_party)
     label_->SetText(current_ime_.short_name + base::UTF8ToUTF16("*"));
   else
     label_->SetText(current_ime_.short_name);
 }
 
 }  // namespace ash