MediaMetrics: Minor logging fixes

Remove extraneous right brace in Time Machine dump.
Do not suppress repeated EVENT properties in the Time Machine.
Use "--" prefix instead of "-" for long dumpsys argv options.

Test: atest mediametrics_tests
Test: adb shell dumpsys media.metrics
Bug: 138583596
Change-Id: I874be909ac08641b14dd12fb2c83de7a276a1796
diff --git a/media/libmediametrics/include/MediaMetricsConstants.h b/media/libmediametrics/include/MediaMetricsConstants.h
index e49917f..fb26fae 100644
--- a/media/libmediametrics/include/MediaMetricsConstants.h
+++ b/media/libmediametrics/include/MediaMetricsConstants.h
@@ -70,14 +70,21 @@
 // Underscores after the AMEDIAMETRICS_PROP_* prefix indicate
 // a "dot" in the property name. For example AMEDIAMETRICS_PROP_VOLUME_LEFT
 // corresponds to "volume.left".
-
+//
+// The property names are camel case, typically a lowercase letter [a-z]
+// followed by one or more characters in the range [a-zA-Z0-9_.].
+// Special symbols such as !@#$%^&*()[]{}<>,:;'"\/?|+-=~ are reserved.
+//
+// A property that ends with a ! will have duplicate values listed instead
+// of suppressed in the Time Machine.
+//
 #define AMEDIAMETRICS_PROP_AUXEFFECTID    "auxEffectId"    // int32 (AudioTrack)
 #define AMEDIAMETRICS_PROP_CHANNELCOUNT   "channelCount"   // int32
 #define AMEDIAMETRICS_PROP_CHANNELMASK    "channelMask"    // int32
 #define AMEDIAMETRICS_PROP_CONTENTTYPE    "contentType"    // string attributes (AudioTrack)
 #define AMEDIAMETRICS_PROP_DURATIONNS     "durationNs"     // int64 duration time span
 #define AMEDIAMETRICS_PROP_ENCODING       "encoding"       // string value of format
-#define AMEDIAMETRICS_PROP_EVENT          "event"          // string value (often func name)
+#define AMEDIAMETRICS_PROP_EVENT          "event!"         // string value (often func name)
 
 // TODO: fix inconsistency in flags: AudioRecord / AudioTrack int32,  AudioThread string
 #define AMEDIAMETRICS_PROP_FLAGS          "flags"