Map isolated uid to host uid when processing log event in statsD.

Test: added test case for isolated uid in Attribution e2e test.
Change-Id: I63d16ebee3e611b1ef0c910e5154cf27766cb330
diff --git a/cmds/statsd/src/logd/LogEvent.cpp b/cmds/statsd/src/logd/LogEvent.cpp
index 49a6e33..6782f3f 100644
--- a/cmds/statsd/src/logd/LogEvent.cpp
+++ b/cmds/statsd/src/logd/LogEvent.cpp
@@ -397,6 +397,14 @@
     return dimensionsValue;
 }
 
+DimensionsValue* LogEvent::findFieldValueOrNull(const Field& field) {
+    auto it = mFieldValueMap.find(field);
+    if (it == mFieldValueMap.end()) {
+        return nullptr;
+    }
+    return &it->second;
+}
+
 string LogEvent::ToString() const {
     ostringstream result;
     result << "{ " << mTimestampNs << " (" << mTagId << ")";