Simplify LogImpl a bit.

services/log/log_impl.h

Index: services/log/log_impl.h
diff --git a/services/log/log_impl.h b/services/log/log_impl.h
index 28a5782e283af8dc25f9aa2401d0791125dce4da..6a94ef29d9e3b519408d3abdb61cb361e35741c8 100644
--- a/services/log/log_impl.h
+++ b/services/log/log_impl.h
@@ -5,8 +5,7 @@
 #ifndef SERVICES_LOG_LOG_IMPL_H_
 #define SERVICES_LOG_LOG_IMPL_H_
 
-#include <stdio.h>
-
+#include <functional>
 #include <string>
 
 #include "base/macros.h"
@@ -22,19 +21,22 @@ class ApplicationConnection;
 namespace log {
 
 // This is an implementation of the log service
-// (see mojo/services/log/interfaces/log.mojom).  It formats incoming messages
-// and writes them to the supplied FILE stream.  It does not take ownership of
-// the FILE stream.
+// (see mojo/services/log/interfaces/log.mojom). It formats incoming messages
+// and "prints" them using a supplied function.
 //
 // This service implementation binds a new Log implementation for each incoming
 // application connection.
 class LogImpl : public Log {
  public:
-  // LogImpl does not take ownership of |out_file|, so |out_file| must live for
-  // the duration of the incoming connection (which is left undefined).
+  // Function that prints the given (fully-formatted) log message.
+  using PrintLogMessageFunction =
+      std::function<void(const std::string& message)>;
+
+  // Note that |print_log_message_function| may be called many times, for the
+  // lifetime of the created object.
   static void Create(ApplicationConnection* connection,
                      InterfaceRequest<Log> request,
-                     FILE* out_file);
+                     PrintLogMessageFunction print_log_message_function);
 
   // |Log| implementation:
   void AddEntry(EntryPtr entry) override;
@@ -42,14 +44,14 @@ class LogImpl : public Log {
  private:
   LogImpl(const std::string& remote_url,
           InterfaceRequest<Log> request,
-          FILE* out_file);
+          PrintLogMessageFunction print_log_message_function);
   ~LogImpl() override;
 
   std::string FormatEntry(const EntryPtr& entry);
 
   const std::string remote_url_;
   StrongBinding<Log> binding_;
-  FILE* out_file_;
+  const PrintLogMessageFunction print_log_message_function_;
 
   DISALLOW_COPY_AND_ASSIGN(LogImpl);
 };