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/BatteryHistoryPreference.java

@@ -21,6 +21,7 @@ import android.support.annotation.VisibleForTesting;
 import android.support.v7.preference.Preference;
 import android.support.v7.preference.PreferenceViewHolder;
 import android.util.AttributeSet;
+import android.view.View;
 import android.widget.TextView;
 import com.android.internal.os.BatteryStatsHelper;
 import com.android.settings.R;
@@ -32,6 +33,10 @@ import com.android.settings.graph.UsageView;
  */
 public class BatteryHistoryPreference extends Preference {
 
+    private CharSequence mSummary;
+    private TextView mSummaryView;
+    private boolean hideSummary;
+
     @VisibleForTesting
     BatteryInfo mBatteryInfo;
 
@@ -48,6 +53,20 @@ public class BatteryHistoryPreference extends Preference {
         }, batteryStats.getStats(), false);
     }
 
+    public void setBottomSummary(CharSequence text) {
+        mSummary = text;
+        if (mSummaryView != null) {
+            mSummaryView.setText(mSummary);
+        }
+    }
+
+    public void hideBottomSummary() {
+        if (mSummaryView != null) {
+            mSummaryView.setVisibility(View.GONE);
+        }
+        hideSummary = true;
+    }
+
     @Override
     public void onBindViewHolder(PreferenceViewHolder view) {
         super.onBindViewHolder(view);
@@ -56,6 +75,13 @@ public class BatteryHistoryPreference extends Preference {
         }
 
         ((TextView) view.findViewById(R.id.charge)).setText(mBatteryInfo.batteryPercentString);
+        mSummaryView = (TextView) view.findViewById(R.id.bottom_summary);
+        if (mSummary != null) {
+            mSummaryView.setText(mSummary);
+        }
+        if (hideSummary) {
+            mSummaryView.setVisibility(View.GONE);
+        }
         UsageView usageView = (UsageView) view.findViewById(R.id.battery_usage);
         usageView.findViewById(R.id.label_group).setAlpha(.7f);
         mBatteryInfo.bindHistory(usageView);