Pass error messages from native messaging to web-app.

remoting/host/native_messaging/log_message_handler.h

Index: remoting/host/native_messaging/log_message_handler.h
diff --git a/remoting/host/native_messaging/log_message_handler.h b/remoting/host/native_messaging/log_message_handler.h
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+++ b/remoting/host/native_messaging/log_message_handler.h
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+// Copyright 2015 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 REMOTING_HOST_NATIVE_MESSAGIN_LOG_HANDLER_H_
+#define REMOTING_HOST_NATIVE_MESSAGIN_LOG_HANDLER_H_
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+#include "base/values.h"
+
+namespace remoting {
+
+// Helper class for logging::SetLogMessageHandler to deliver log messages to
+// a consistent thread in a thread-safe way and in a format suitable for sending
+// over a Native Messaging channel.
+class LogMessageHandler {
+ public:
+  typedef base::Callback<void (scoped_ptr<base::Value> message)> Delegate;
+
+  explicit LogMessageHandler(const Delegate& delegate);
+  ~LogMessageHandler();
+
+  static const char* kDebugMessageTypeName;
+
+ private:
+  static bool OnLogMessage(
+      int severity, const char* file, int line,
+      size_t message_start, const std::string& str);
+  void PostLogMessageToCorrectThread(
+      int severity, const char* file, int line,
+      size_t message_start, const std::string& str);
+  void SendLogMessageToClient(
+      int severity, const char* file, int line,
+      size_t message_start, const std::string& str);
+
+  Delegate delegate_;
+  bool suppress_logging_;
+  scoped_refptr<base::SingleThreadTaskRunner> caller_task_runner_;
+  logging::LogMessageHandlerFunction previous_log_message_handler_;
+  base::WeakPtrFactory<LogMessageHandler> weak_ptr_factory_;
+};
+
+}  // namespace remoting
+
+#endif