logd: statistics add logspan

Logspan down to the millisecond.  Show a percentage if trimmed by
Chatty messages, a subspan from the newest to the newest chatty in
the log buffer.  Sniff stats.add(elem), stats.subtract(elem) and
stats.dropped(elem) to generate the logspan data.

Test: gTest liblog-unit-tests, logd-unit-tests and logcat-unit-tests
Test: manual check Logspan statistics for being in range, added
      temporary internal instrumentation to confirm expectations.
Bug: 37254265
Change-Id: I09c0d9375d5580315543c747b37976f9eeb9e408
diff --git a/logd/LogStatistics.h b/logd/LogStatistics.h
index e171e4a..e6f01d6 100644
--- a/logd/LogStatistics.h
+++ b/logd/LogStatistics.h
@@ -28,6 +28,7 @@
 
 #include <android-base/stringprintf.h>
 #include <android/log.h>
+#include <log/log_time.h>
 #include <private/android_filesystem_config.h>
 
 #include "LogBufferElement.h"
@@ -520,6 +521,9 @@
     size_t mDroppedElements[LOG_ID_MAX];
     size_t mSizesTotal[LOG_ID_MAX];
     size_t mElementsTotal[LOG_ID_MAX];
+    log_time mOldest[LOG_ID_MAX];
+    log_time mNewest[LOG_ID_MAX];
+    log_time mNewestDropped[LOG_ID_MAX];
     static size_t SizesTotal;
     bool enable;