Include timer metrics into trace

This allows us to see from a trace how long operations took that are
captured by timer metrics.

Example log entry on push:
[2018-08-29 10:28:37,080] [ReceiveCommits-1] TRACE com.google.gerrit.metrics.Timer0.Context : http/server/rest_api/change_json/to_change_info_latency took 24ms [CONTEXT forced=true RECEIVE_ID="foo-1535531316769-7edf2a7b" TRACE_ID="1535531316773-7edf2a7b" ]

Change-Id: Ib0024cce95693d99781aee8a2b78b777c7c4ce3b
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/com/google/gerrit/metrics/Timer0.java

@@ -16,6 +16,7 @@ package com.google.gerrit.metrics;
 
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 
+import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.extensions.registration.RegistrationHandle;
 import java.util.concurrent.TimeUnit;
 
@@ -31,6 +32,8 @@ import java.util.concurrent.TimeUnit;
  */
 public abstract class Timer0 implements RegistrationHandle {
   public static class Context extends TimerContext {
+    private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
     private final Timer0 timer;
 
     Context(Timer0 timer) {
@@ -39,10 +42,17 @@ public abstract class Timer0 implements RegistrationHandle {
 
     @Override
     public void record(long elapsed) {
+      logger.atFinest().log("%s took %dms", timer.name, TimeUnit.NANOSECONDS.toMillis(elapsed));
       timer.record(elapsed, NANOSECONDS);
     }
   }
 
+  protected final String name;
+
+  public Timer0(String name) {
+    this.name = name;
+  }
+
   /**
    * Begin a timer for the current block, value will be recorded when closed.
    *