cros: Update charging not reliable battery status

Don't display the "charging not reliable" battery status in the 
non-charging-non-discharging state, as that can happen normally in
some circumstances. Also, update the string to be more human-friendly.

BUG=246336
TEST=manual, see bug

Review URL: https://chromiumcodereview.appspot.com/16057022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@203952 0039d316-1c4b-4281-b951-d872f2087c98

ash/ash_strings.grd

@@ -426,7 +426,7 @@ Press Shift + Alt to switch.
         <ph name="hour">$1<ex>2</ex></ph>:<ph name="minute">$2<ex>53</ex></ph> until full
       </message>
       <message name="IDS_ASH_STATUS_TRAY_BATTERY_CHARGING_UNRELIABLE" desc="The label in the tray dialog to indicate that battery charging is unreliable.">
-        Charging not reliable
+        Low-power charger
       </message>
       <message name="IDS_ASH_STATUS_TRAY_BATTERY_FULL_CHARGE_ACCESSIBLE" desc="The message used by accessibility to show battery is full and charging.">
         Battery is full and charging.
@@ -450,7 +450,7 @@ Press Shift + Alt to switch.
         <ph name="hour">$1<ex> 1 hour</ex></ph> and <ph name="minute">$2<ex>15 minutes</ex></ph>
       </message>
       <message name="IDS_ASH_STATUS_TRAY_BATTERY_CHARGING_UNRELIABLE_ACCESSIBLE" desc="The message used by accessibility to indicate that battery charging is unreliable.">
-        Plugged in to a non-standard power supply. Battery charging may not be reliable.
+        Plugged in to a low-power charger. Battery charging may not be reliable.
       </message>
       <message name="IDS_ASH_STATUS_TRAY_HELP" desc="The accessible text for the help button.">
         Help

ash/system/chromeos/power/tray_power.cc

@@ -217,11 +217,12 @@ TrayPower::~TrayPower() {
 // static
 bool TrayPower::IsBatteryChargingUnreliable(
     const chromeos::PowerSupplyStatus& supply_status) {
-  return
-      supply_status.battery_state ==
-          PowerSupplyStatus::NEITHER_CHARGING_NOR_DISCHARGING ||
-      supply_status.battery_state ==
-          PowerSupplyStatus::CONNECTED_TO_USB;
+  // Sometimes devices can get into a state where the battery is almost fully
+  // charged and the power subsystem reports "neither charging nor discharging"
+  // despite the battery not at 100%. For now, only report unreliable charging
+  // on USB.
+  // TODO(derat): Update this when the power manager code is refactored for M29.
+  return supply_status.battery_state == PowerSupplyStatus::CONNECTED_TO_USB;
 }
 
 // static