Add MultiStateCounter.addValue and make updateValue return delta

Bug: 197162116
Test: atest libbattery_test
Change-Id: I790ed0b805a88aa6ee9659f8494af8edf693d931
diff --git a/libs/battery/MultiStateCounter.h b/libs/battery/MultiStateCounter.h
index e1ee07c..112fb85 100644
--- a/libs/battery/MultiStateCounter.h
+++ b/libs/battery/MultiStateCounter.h
@@ -62,7 +62,13 @@
 
     void setValue(state_t state, const T& value);
 
-    void updateValue(const T& value, time_t timestamp);
+    /**
+     * Updates the value for the current state and returns the delta from the previously
+     * set value.
+     */
+    const T& updateValue(const T& value, time_t timestamp);
+
+    void addValue(const T& value);
 
     void reset();
 
@@ -161,7 +167,7 @@
 }
 
 template <class T>
-void MultiStateCounter<T>::updateValue(const T& value, time_t timestamp) {
+const T& MultiStateCounter<T>::updateValue(const T& value, time_t timestamp) {
     // If the counter is disabled, we ignore the update, except when the counter got disabled after
     // the previous update, in which case we still need to pick up the residual delta.
     if (isEnabled || lastUpdateTimestamp < lastStateChangeTimestamp) {
@@ -195,6 +201,16 @@
     }
     lastValue = value;
     lastUpdateTimestamp = timestamp;
+    return deltaValue;
+}
+
+template <class T>
+void MultiStateCounter<T>::addValue(const T& value) {
+    if (!isEnabled) {
+        return;
+    }
+
+    add(&states[currentState].counter, value, 1 /* numerator */, 1 /* denominator */);
 }
 
 template <class T>
@@ -242,7 +258,9 @@
     } else {
         str << " currentState: none";
     }
-
+    if (!isEnabled) {
+        str << " disabled";
+    }
     return str.str();
 }