Camera: Add user tag to camera action event

The user tag set by CaptureRequest.setTag() is passed to cameraservice.
The cameraservice saves the latest tag's string description into the
camera action event's session data.

Test: ./out/host/linux-x86/bin/statsd_testdrive 227
Bug: 223671217
Change-Id: I604d8b3bd3895c330de5b02498c7eb3ed8e05ed8
diff --git a/services/camera/libcameraservice/api2/CameraDeviceClient.h b/services/camera/libcameraservice/api2/CameraDeviceClient.h
index 9d1deb1..3af0b80 100644
--- a/services/camera/libcameraservice/api2/CameraDeviceClient.h
+++ b/services/camera/libcameraservice/api2/CameraDeviceClient.h
@@ -349,6 +349,9 @@
 
     // Override the camera characteristics for performance class primary cameras.
     bool mOverrideForPerfClass;
+
+    // The string representation of object passed into CaptureRequest.setTag.
+    std::string mUserTag;
 };
 
 }; // namespace android