BatteryStatus: fix chargingTime() to follow the specification.

Source/modules/battery/BatteryManager.cpp

Index: Source/modules/battery/BatteryManager.cpp
diff --git a/Source/modules/battery/BatteryManager.cpp b/Source/modules/battery/BatteryManager.cpp
index aae81bcf1448b25da6e871ea668cfcd90650432e..3eb3b219f749f2ac41339bd71b4e5cc65bc9c20b 100644
--- a/Source/modules/battery/BatteryManager.cpp
+++ b/Source/modules/battery/BatteryManager.cpp
@@ -34,9 +34,16 @@ bool BatteryManager::charging()
 
 double BatteryManager::chargingTime()
 {
-    if (!m_batteryStatus || !m_batteryStatus->charging())
+    if (!m_batteryStatus)
+        return 0;
+
+    if (!m_batteryStatus->charging())
         return std::numeric_limits<double>::infinity();
 
+    // The spec requires that if level == 1.0, chargingTime == 0 but this has to
+    // be implement by the backend. Adding this assert will help enforcing it.
+    ASSERT(level() != 1.0 && m_batteryStatus->chargingTime() == 0.0);
+
     return m_batteryStatus->chargingTime();
 }