Help inline LogMessage::stream method.

A very simple method that should be safely inlined by compiler.

Change-Id: I7a2fa41d566e36b30b1afd6a2f6b0c2f986dc46f
diff --git a/src/base/logging.h b/src/base/logging.h
index f250ce0..8d89e4d 100644
--- a/src/base/logging.h
+++ b/src/base/logging.h
@@ -184,8 +184,12 @@
   LogMessage(const char* file, int line, LogSeverity severity, int error)
     : data_(new LogMessageData(file, line, severity, error)) {
   }
+
   ~LogMessage() LOCKS_EXCLUDED(Locks::logging_lock_);
-  std::ostream& stream();
+
+  std::ostream& stream() {
+    return data_->buffer;
+  }
 
  private:
   static void LogLine(const LogMessageData& data, const char*);