Implement LoadLog, and hook up HostResolverImpl to LoadLog....

net/base/load_log_util.h

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_LOAD_LOG_UTIL_H_
+#define NET_BASE_LOAD_LOG_UTIL_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "net/base/load_log.h"
+
+namespace net {
+
+// The LoadLogUtil utility class contains methods to analyze and visualize
+// LoadLogs.
+
+class LoadLogUtil {
+ public:
+  struct EventDuration {
+    LoadLog::EventType event;
+    base::TimeDelta duration;
+  };
+  typedef std::vector<EventDuration> EventDurationList;
+
+  // Builds a pretty printed ASCII tree showing the chronological order
+  // of events.
+  //
+  // The indentation reflects hiearchy, with the duration of each indented
+  // block noted on the right. The timestamp (tick count in milliseconds)
+  // is noted in the left column.
+  //
+  // This detailed view of what went into servicing a request can be used
+  // in logs, and is copy-pastable by users, for attaching to bug reports.
+  //
+  // Example A:
+  //
+  //     t=0: +Event1       [dt = 8]
+  //     t=1:   +Event2     [dt = 0]
+  //     t=1:      EventX
+  //     t=1:   -Event2
+  //     t=4:   +Event3     [dt = 2]
+  //     t=6:   -Event3
+  //     t=6:   +Event2     [dt = 1]
+  //     t=7:   -Event2
+  //     t=8:    EventY
+  //     t=8: -Event1
+  //
+  // Here we can see that:
+  //   - Event1 started at t=0 and ended at t=8; the duration was 8 time units.
+  //   - Event2 took place while Event1 was in progress, and was repeated
+  //     at t=1 and t=6.
+  //   - EventX took place while (the first) Event2 was in progress.
+  //   - Event3 started and ended at the same time, taking 0 time.
+  //   - EventY took place right before Event1 finished, at t=8
+  //
+  // In general the rules are:
+  //   - Log entries added by BeginEvent() are prefixed with a '+' and
+  //     start an indentation block.
+  //   - Log entries added by EndEvent() are prefixed with a '-' and
+  //     finish an indentation block.
+  //   - Log entries added by AddEvent() have no prefix.
+  //   - Time units are given as milliseconds.
+  //
+  static std::string PrettyPrintAsEventTree(const LoadLog* log);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(LoadLogUtil);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_LOAD_LOG_UTIL_H_