Add histogram entries (timestamp and flush)

Add functions to write these entries into log

Add functionality to dump them in dumpsys

Bug: 36490717
Test: Write format entries and histogram entries in the log.
      Verify that format entries and histograms are dumped correctly

Change-Id: I2e0b48c63031e62875c08461b98653ecfe1442be
diff --git a/services/medialog/MediaLogService.h b/services/medialog/MediaLogService.h
index c6b99f1..06c721f 100644
--- a/services/medialog/MediaLogService.h
+++ b/services/medialog/MediaLogService.h
@@ -49,7 +49,8 @@
     // Internal dump
     static const int kDumpLockRetries = 50;
     static const int kDumpLockSleepUs = 20000;
-    static const size_t kMergeBufferSize = 16 * 1024; // TODO determine good value for this
+    // Size of merge buffer, in bytes
+    static const size_t kMergeBufferSize = 64 * 1024; // TODO determine good value for this
     static bool dumpTryLock(Mutex& mutex);
 
     Mutex               mLock;