DevTools: do not clear console when preserving log

third_party/WebKit/Source/devtools/front_end/console/ConsoleViewMessage.js

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  * Copyright (C) 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
@@ skipping 186 matching lines @@
   _buildMessage() {
     var messageElement;
     var messageText = this._message.messageText;
     if (this._message.source === ConsoleModel.ConsoleMessage.MessageSource.ConsoleAPI) {
       switch (this._message.type) {
         case ConsoleModel.ConsoleMessage.MessageType.Trace:
           messageElement = this._format(this._message.parameters || ['console.trace']);
           break;
         case ConsoleModel.ConsoleMessage.MessageType.Clear:
           messageElement = createElementWithClass('span', 'console-info');
-          messageElement.textContent = Common.UIString('Console was cleared');
+          messageElement.textContent = ConsoleModel.ConsoleModel.canMessageClearConsole(this._message) ?
+              Common.UIString('Console was cleared') :
+              Common.UIString('console.clear() was prevented from non-main frame or \'Preserve log\'');

[pfeldman, 2017/07/12 21:17:28]

This does not sounds like a consistent sentence to me.

`console.clear() was prevented due to 'Preserve log'` or
`console.clear() from iframe was ignored`

[luoe, 2017/07/13 00:42:03]

Done.

+          messageElement.title =
+              Common.UIString('Clear all messages with ' + UI.shortcutRegistry.shortcutTitleForAction('console.clear'));
           break;
         case ConsoleModel.ConsoleMessage.MessageType.Assert:
           var args = [Common.UIString('Assertion failed:')];
           if (this._message.parameters)
             args = args.concat(this._message.parameters);
           messageElement = this._format(args);
           break;
         case ConsoleModel.ConsoleMessage.MessageType.Dir:
           var obj = this._message.parameters ? this._message.parameters[0] : undefined;
           var args = ['%O', obj];
@@ skipping 1117 matching lines @@
     }
     return this._element;
   }
 };
 
 /**
  * @const
  * @type {number}
  */
 Console.ConsoleViewMessage.MaxLengthForLinks = 40;