MediaMetrics: Update Item serialization code

Add for bounds checking errors
Update key checks to omit length, use C primitive types

Test: atest mediametrics_tests, adb shell dumpsys media.metrics
Change-Id: I1e6d5bd7a9611f6d59e15a1dbebc646405e5a018
diff --git a/media/libmediametrics/MediaMetrics.cpp b/media/libmediametrics/MediaMetrics.cpp
index 360ae0c..cf268e0 100644
--- a/media/libmediametrics/MediaMetrics.cpp
+++ b/media/libmediametrics/MediaMetrics.cpp
@@ -195,6 +195,6 @@
 bool mediametrics_getAttributes(mediametrics_handle_t handle, char **buffer, size_t *length) {
     android::MediaAnalyticsItem *item = (android::MediaAnalyticsItem *) handle;
     if (item == NULL) return false;
-    return item->dumpAttributes(buffer, length);
+    return item->writeToByteString(buffer, length) == android::NO_ERROR;
 
 }