Add TtsSpan for formatted time.

Talk back will read "Used for 3m" as "Used for 3 meters", but
it will read "Used for 3h 3m" correctly.

This cl add specific Ttsspan if the time only contains "minute"

Bug: 36379530
Test: Run SettingsRoboTests

Change-Id: I033575938cce24221980dddd9d66be4e18804541

src/com/android/settings/fuelgauge/PowerGaugePreference.java

@@ -79,11 +79,15 @@ public class PowerGaugePreference extends TintablePreference {
         return mProgress.toString();
     }
 
-    public void setSubtitle(String subtitle) {
+    public void setSubtitle(CharSequence subtitle) {
         mProgress = subtitle;
         notifyChanged();
     }
 
+    public CharSequence getSubtitle() {
+        return mProgress;
+    }
+
     BatteryEntry getInfo() {
         return mInfo;
     }