Don't show "Service Worker Fallback Required" error message in DevTools console.

Source/core/frame/FrameConsole.cpp

 /*
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * 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
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 111 matching lines @@
         stackTrace = FrameConsole::formatStackTraceString(consoleMessage->message(), reportedCallStack);
     frame().chromeClient().addMessageToConsole(m_frame, consoleMessage->source(), consoleMessage->level(), consoleMessage->message(), lineNumber, messageURL, stackTrace);
 }
 
 void FrameConsole::reportResourceResponseReceived(DocumentLoader* loader, unsigned long requestIdentifier, const ResourceResponse& response)
 {
     if (!loader)
         return;
     if (response.httpStatusCode() < 400)
         return;
+    if (response.wasFallbackRequiredByServiceWorker())
+        return;
     String message = "Failed to load resource: the server responded with a status of " + String::number(response.httpStatusCode()) + " (" + response.httpStatusText() + ')';
     RefPtrWillBeRawPtr<ConsoleMessage> consoleMessage = ConsoleMessage::create(NetworkMessageSource, ErrorMessageLevel, message, response.url().string());
     consoleMessage->setRequestIdentifier(requestIdentifier);
     addMessage(consoleMessage.release());
 }
 
 String FrameConsole::formatStackTraceString(const String& originalMessage, PassRefPtrWillBeRawPtr<ScriptCallStack> callStack)
 {
     StringBuilder stackTrace;
     for (size_t i = 0; i < callStack->size(); ++i) {
@@ skipping 60 matching lines @@
     consoleMessage->setRequestIdentifier(requestIdentifier);
     storage->reportMessage(m_frame->document(), consoleMessage.release());
 }
 
 DEFINE_TRACE(FrameConsole)
 {
     visitor->trace(m_frame);
 }
 
 } // namespace blink