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/utils/SessionStatsBuilder.h b/services/camera/libcameraservice/utils/SessionStatsBuilder.h
index c23abb6..2936531 100644
--- a/services/camera/libcameraservice/utils/SessionStatsBuilder.h
+++ b/services/camera/libcameraservice/utils/SessionStatsBuilder.h
@@ -84,6 +84,7 @@
     int64_t mErrorResultCount;
     bool mCounterStopped;
     bool mDeviceError;
+    std::string mUserTag;
     // Map from stream id to stream statistics
     std::map<int, StreamStats> mStatsMap;
 };