health: registerCallback() and getHealthInfo() does not notify all callbacks

registerCallback() and getHealthInfo() unintentionally broadcast
health info to all callbacks, which has a performance impact.

* registerCallback() still invokes the new callback immediately
* getHealthInfo() does not call any callbacks at all.

Test: VTS test call getHealthInfo does not invoke update()
Bug: 117167903
Change-Id: Ida99fdd73831e747fbf2d65089c7c0e7661fe7c4
diff --git a/health/2.0/default/include/health2/Health.h b/health/2.0/default/include/health2/Health.h
index b960358..6410474 100644
--- a/health/2.0/default/include/health2/Health.h
+++ b/health/2.0/default/include/health2/Health.h
@@ -64,6 +64,10 @@
     std::unique_ptr<BatteryMonitor> battery_monitor_;
 
     bool unregisterCallbackInternal(const sp<IBase>& cb);
+
+    // update() and only notify the given callback, but none of the other callbacks.
+    // If cb is null, do not notify any callback at all.
+    Return<Result> updateAndNotify(const sp<IHealthInfoCallback>& cb);
 };
 
 }  // namespace implementation