Add info string to advanced battery usage page

This CL adds an FYI string under the battery graph to let users
know that their current estimate is coming from the enhanced
estimate provider when it is enabled.

Test: Robotests
Bug: 38399654
Change-Id: If5cd622ef0251a5a483cef870fc2261369e14845

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

@@ -69,9 +69,9 @@ public class PowerUsageAdvanced extends PowerUsageBase {
             UsageType.UNACCOUNTED,
             UsageType.OVERCOUNTED};
 
+    @VisibleForTesting BatteryHistoryPreference mHistPref;
+    @VisibleForTesting PreferenceGroup mUsageListGroup;
     private BatteryUtils mBatteryUtils;
-    private BatteryHistoryPreference mHistPref;
-    private PreferenceGroup mUsageListGroup;
     private PowerUsageFeatureProvider mPowerUsageFeatureProvider;
     private PackageManager mPackageManager;
     private UserManager mUserManager;
@@ -170,6 +170,14 @@ public class PowerUsageAdvanced extends PowerUsageBase {
         }
         updatePreference(mHistPref);
         refreshPowerUsageDataList(mStatsHelper, mUsageListGroup);
+
+        if (mPowerUsageFeatureProvider.isEnhancedBatteryPredictionEnabled(context)) {
+            mHistPref.setBottomSummary(
+                    mPowerUsageFeatureProvider.getAdvancedUsageScreenInfoString());
+        } else {
+            mHistPref.hideBottomSummary();
+        }
+
         BatteryEntry.startRequestQueue();
     }