diff -r 000000000000 -r 6474c204b198 dom/battery/BatteryManager.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/battery/BatteryManager.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,144 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 <limits>
+#include "BatteryManager.h"
+#include "Constants.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/Hal.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/dom/BatteryManagerBinding.h"
+#include "nsIDOMClassInfo.h"
+
+/**
+ * We have to use macros here because our leak analysis tool things we are
+ * leaking strings when we have |static const nsString|. Sad :(
+ */
+#define LEVELCHANGE_EVENT_NAME           NS_LITERAL_STRING("levelchange")
+#define CHARGINGCHANGE_EVENT_NAME        NS_LITERAL_STRING("chargingchange")
+#define DISCHARGINGTIMECHANGE_EVENT_NAME NS_LITERAL_STRING("dischargingtimechange")
+#define CHARGINGTIMECHANGE_EVENT_NAME    NS_LITERAL_STRING("chargingtimechange")
+
+namespace mozilla {
+namespace dom {
+namespace battery {
+
+BatteryManager::BatteryManager(nsPIDOMWindow* aWindow)
+  : DOMEventTargetHelper(aWindow)
+  , mLevel(kDefaultLevel)
+  , mCharging(kDefaultCharging)
+  , mRemainingTime(kDefaultRemainingTime)
+{
+}
+
+void
+BatteryManager::Init()
+{
+  hal::RegisterBatteryObserver(this);
+
+  hal::BatteryInformation batteryInfo;
+  hal::GetCurrentBatteryInformation(&batteryInfo);
+
+  UpdateFromBatteryInfo(batteryInfo);
+}
+
+void
+BatteryManager::Shutdown()
+{
+  hal::UnregisterBatteryObserver(this);
+}
+
+JSObject*
+BatteryManager::WrapObject(JSContext* aCx)
+{
+  return BatteryManagerBinding::Wrap(aCx, this);
+}
+
+double
+BatteryManager::DischargingTime() const
+{
+  if (mCharging || mRemainingTime == kUnknownRemainingTime) {
+    return std::numeric_limits<double>::infinity();
+  }
+
+  return mRemainingTime;
+}
+
+double
+BatteryManager::ChargingTime() const
+{
+  if (!mCharging || mRemainingTime == kUnknownRemainingTime) {
+    return std::numeric_limits<double>::infinity();
+  }
+
+  return mRemainingTime;
+}
+
+void
+BatteryManager::UpdateFromBatteryInfo(const hal::BatteryInformation& aBatteryInfo)
+{
+  mLevel = aBatteryInfo.level();
+  mCharging = aBatteryInfo.charging();
+  mRemainingTime = aBatteryInfo.remainingTime();
+
+  // Add some guards to make sure the values are coherent.
+  if (mLevel == 1.0 && mCharging == true &&
+      mRemainingTime != kDefaultRemainingTime) {
+    mRemainingTime = kDefaultRemainingTime;
+    NS_ERROR("Battery API: When charging and level at 1.0, remaining time "
+             "should be 0. Please fix your backend!");
+  }
+}
+
+void
+BatteryManager::Notify(const hal::BatteryInformation& aBatteryInfo)
+{
+  double previousLevel = mLevel;
+  bool previousCharging = mCharging;
+  double previousRemainingTime = mRemainingTime;
+
+  UpdateFromBatteryInfo(aBatteryInfo);
+
+  if (previousCharging != mCharging) {
+    DispatchTrustedEvent(CHARGINGCHANGE_EVENT_NAME);
+  }
+
+  if (previousLevel != mLevel) {
+    DispatchTrustedEvent(LEVELCHANGE_EVENT_NAME);
+  }
+
+  /*
+   * There are a few situations that could happen here:
+   * 1. Charging state changed:
+   *   a. Previous remaining time wasn't unkwonw, we have to fire an event for
+   *      the change.
+   *   b. New remaining time isn't unkwonw, we have to fire an event for it.
+   * 2. Charging state didn't change but remainingTime did, we have to fire
+   *    the event that correspond to the current charging state.
+   */
+  if (mCharging != previousCharging) {
+    if (previousRemainingTime != kUnknownRemainingTime) {
+      DispatchTrustedEvent(previousCharging ? CHARGINGTIMECHANGE_EVENT_NAME
+                                            : DISCHARGINGTIMECHANGE_EVENT_NAME);
+    }
+    if (mRemainingTime != kUnknownRemainingTime) {
+      DispatchTrustedEvent(mCharging ? CHARGINGTIMECHANGE_EVENT_NAME
+                                     : DISCHARGINGTIMECHANGE_EVENT_NAME);
+    }
+  } else if (previousRemainingTime != mRemainingTime) {
+    DispatchTrustedEvent(mCharging ? CHARGINGTIMECHANGE_EVENT_NAME
+                                   : DISCHARGINGTIMECHANGE_EVENT_NAME);
+  }
+}
+
+/* static */ bool
+BatteryManager::HasSupport()
+{
+  return Preferences::GetBool("dom.battery.enabled", true);
+}
+
+} // namespace battery
+} // namespace dom
+} // namespace mozilla