port metrics_logger to v2 format

Bug: 34450377
Test: manual, needs to be a cross-language test
Change-Id: Ib89a48f2c52428deff863b0c28f3c10e7333c8a2

libmetricslogger/Android.bp

@@ -22,7 +22,7 @@ cc_defaults {
 
         // 524291 corresponds to sysui_histogram, from
         // frameworks/base/core/java/com/android/internal/logging/EventLogTags.logtags
-        "-DHISTOGRAM_LOG_TAG=524291",
+        "-DHISTOGRAM_LOG_TAG=524292",
     ],
 }
 

libmetricslogger/include/metricslogger/metrics_logger.h

@@ -24,5 +24,14 @@ namespace metricslogger {
 // buffer.
 void LogHistogram(const std::string& event, int32_t data);
 
+// TODO: replace these with the metric_logger.proto definitions
+enum {
+  LOGBUILDER_CATEGORY = 757,
+  LOGBUILDER_NAME = 799,
+  LOGBUILDER_BUCKET = 801,
+  LOGBUILDER_VALUE = 802,
+  LOGBUILDER_HISTOGRAM = 804,
+};
+
 }  // namespace metricslogger
 }  // namespace android

libmetricslogger/metrics_logger.cpp

@@ -23,9 +23,14 @@
 namespace android {
 namespace metricslogger {
 
+// Mirror com.android.internal.logging.MetricsLogger#histogram().
 void LogHistogram(const std::string& event, int32_t data) {
   android_log_event_list log(HISTOGRAM_LOG_TAG);
-  log << event << data << LOG_ID_EVENTS;
+  log << LOGBUILDER_CATEGORY << LOGBUILDER_HISTOGRAM
+      << LOGBUILDER_NAME << event
+      << LOGBUILDER_BUCKET << data
+      << LOGBUILDER_VALUE << 1
+      << LOG_ID_EVENTS;
 }
 
 }  // namespace metricslogger