Only update system power indicators on change

ash/system/power/power_status_view.cc

 // Copyright (c) 2012 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/system/power/power_status_view.h"
 
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/system/power/tray_power.h"
 #include "ash/system/tray/tray_constants.h"
@@ skipping 21 matching lines @@
 const int kPaddingBetweenBatteryStatusAndIcon = 3;
 }  // namespace
 
 PowerStatusView::PowerStatusView(ViewType view_type,
                                  bool default_view_right_align)
     : default_view_right_align_(default_view_right_align),
       status_label_(NULL),
       time_label_(NULL),
       time_status_label_(NULL),
       icon_(NULL),
+      icon_image_index_(-1),
       view_type_(view_type) {
   if (view_type == VIEW_DEFAULT) {
     time_status_label_ = new views::Label;
     LayoutDefaultView();
   } else {
     status_label_ = new views::Label;
     time_label_ = new views::Label;
     LayoutNotificationView();
   }
   Update();
@@ skipping 120 matching lines @@
                 static_cast<int>(supply_status_.battery_percentage))));
   }
 
   if (supply_status_.is_calculating_battery_time) {
     time_label_->SetText(
         ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
             IDS_ASH_STATUS_TRAY_BATTERY_CALCULATING));
   } else if (hour || min) {
     if (supply_status_.line_power_on) {
       time_label_->SetText(
-        l10n_util::GetStringFUTF16(
-            IDS_ASH_STATUS_TRAY_BATTERY_TIME_UNTIL_FULL,
-            base::IntToString16(hour),
-            base::IntToString16(min)));
+          l10n_util::GetStringFUTF16(
+              IDS_ASH_STATUS_TRAY_BATTERY_TIME_UNTIL_FULL,
+              base::IntToString16(hour),
+              base::IntToString16(min)));
     } else {
       // This is a low battery warning, which prompts user when battery
       // time left is not much (ie in minutes).
       min = hour * 60 + min;
       ShellDelegate* delegate = Shell::GetInstance()->delegate();
       if (delegate) {
         time_label_->SetText(delegate->GetTimeRemainingString(
-                                 base::TimeDelta::FromMinutes(min)));
+            base::TimeDelta::FromMinutes(min)));
       } else {
         time_label_->SetText(string16());
       }
     }
   } else {
     time_label_->SetText(string16());
   }
-
 }
 
 void PowerStatusView::UpdateIcon() {
   if (icon_) {
-    icon_->SetImage(TrayPower::GetBatteryImage(supply_status_, ICON_DARK,
-                                               icon_->GetImage()));
+    int index = TrayPower::GetBatteryImageIndex(supply_status_);
+    if (icon_image_index_ != index) {
+      icon_image_index_ = index;
+      if (icon_image_index_ == -1) {
+        // Default in case supply_status_ is uncertain.
+        icon_->SetImage(icon_->GetImage());

[Daniel Erat, 2012/09/11 23:31:04]

didn't see any explanation for this: it looks like you're telling the icon to
use the same image that it's already using.  if this has some other side effect,
add a comment explaining what it is.

same question goes for two places in tray_power.cc.

+      } else {
+        icon_->SetImage(
+            TrayPower::GetBatteryImage(icon_image_index_, ICON_DARK));
+      }
+    }
     icon_->SetVisible(true);
   }
 }
 
 void PowerStatusView::Update() {
   UpdateText();
   UpdateIcon();
 }
 
 void PowerStatusView::ChildPreferredSizeChanged(views::View* child) {
   PreferredSizeChanged();
 }
 
 gfx::Size PowerStatusView::GetPreferredSize() {
   gfx::Size size = views::View::GetPreferredSize();
   return gfx::Size(size.width(), kTrayPopupItemHeight);
 }
 
 }  // namespace internal
 }  // namespace ash