First cut at UI for saving net_logs data into a temporary file on

chrome/browser/net/net_log_logger.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/net/net_log_logger.h"
 
 #include <stdio.h>
 
 #include "base/file_util.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/values.h"
 #include "chrome/browser/ui/webui/net_internals/net_internals_ui.h"
 
-NetLogLogger::NetLogLogger(const FilePath &log_path) {
+NetLogLogger::NetLogLogger(const FilePath &log_path) : net_log_(NULL) {
   if (!log_path.empty()) {
     base::ThreadRestrictions::ScopedAllowIO allow_io;
     FILE* fp = file_util::OpenFile(log_path, "w");
     if (!fp) {
       LOG(ERROR) << "Could not open file " << log_path.value()
                  << " for net logging";
       return;
     }
     file_.Set(fp);
 
     // Write constants to the output file.  This allows loading files that have
     // different source and event types, as they may be added and removed
     // between Chrome versions.
     scoped_ptr<Value> value(NetInternalsUI::GetConstants());
     std::string json;
     base::JSONWriter::Write(value.get(), &json);
     fprintf(file_.get(), "{\"constants\": %s,\n", json.c_str());
     fprintf(file_.get(), "\"events\": [\n");
   }
 }
 
 NetLogLogger::~NetLogLogger() {
 }
 
 void NetLogLogger::StartObserving(net::NetLog* net_log) {
   net_log->AddThreadSafeObserver(this, net::NetLog::LOG_ALL_BUT_BYTES);
+  net_log_ = net_log;
+}
+
+void NetLogLogger::StopObserving() {
+  DCHECK(net_log_);
+  net_log_->RemoveThreadSafeObserver(this);
+  net_log_ = NULL;
 }
 
 void NetLogLogger::OnAddEntry(const net::NetLog::Entry& entry) {
   scoped_ptr<Value> value(entry.ToValue());
   // Don't pretty print, so each JSON value occupies a single line, with no
   // breaks (Line breaks in any text field will be escaped).  Using strings
   // instead of integer identifiers allows logs from older versions to be
   // loaded, though a little extra parsing has to be done when loading a log.
   std::string json;
   base::JSONWriter::Write(value.get(), &json);
   if (!file_.get()) {
     VLOG(1) << json;
   } else {
     fprintf(file_.get(), "%s,\n", json.c_str());
   }
 }