Add "lax mixed content checking" runtime flag.

Source/core/xml/XMLHttpRequest.cpp

 /*
  *  Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005-2007 Alexey Proskuryakov <ap@webkit.org>
  *  Copyright (C) 2007, 2008 Julien Chaffraix <jchaffraix@webkit.org>
  *  Copyright (C) 2008, 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
@@ skipping 843 matching lines @@
     options.preflightPolicy = uploadEvents ? ForcePreflight : ConsiderPreflight;
     options.crossOriginRequestPolicy = UseAccessControl;
     options.initiator = FetchInitiatorTypeNames::xmlhttprequest;
     options.contentSecurityPolicyEnforcement = ContentSecurityPolicy::shouldBypassMainWorld(&executionContext) ? DoNotEnforceContentSecurityPolicy : EnforceConnectSrcDirective;
     options.timeoutMilliseconds = m_timeoutMilliseconds;
 
     ResourceLoaderOptions resourceLoaderOptions;
     resourceLoaderOptions.allowCredentials = (m_sameOriginRequest || m_includeCredentials) ? AllowStoredCredentials : DoNotAllowStoredCredentials;
     resourceLoaderOptions.credentialsRequested = m_includeCredentials ? ClientRequestedCredentials : ClientDidNotRequestCredentials;
     resourceLoaderOptions.securityOrigin = securityOrigin();
-    resourceLoaderOptions.mixedContentBlockingTreatment = TreatAsActiveContent;
+    resourceLoaderOptions.mixedContentBlockingTreatment = RuntimeEnabledFeatures::laxMixedContentCheckingEnabled() ? TreatAsPassiveContent : TreatAsActiveContent;
 
     // When responseType is set to "blob", we redirect the downloaded data to a
     // file-handle directly.
     if (responseTypeCode() == ResponseTypeBlob) {
         request.setDownloadToFile(true);
         resourceLoaderOptions.dataBufferingPolicy = DoNotBufferData;
     }
 
     m_exceptionCode = 0;
     m_error = false;
@@ skipping 587 matching lines @@
 {
     visitor->trace(m_responseBlob);
     visitor->trace(m_responseStream);
     visitor->trace(m_responseDocument);
     visitor->trace(m_progressEventThrottle);
     visitor->trace(m_upload);
     XMLHttpRequestEventTarget::trace(visitor);
 }
 
 } // namespace WebCore