Introduce a field trial to strictly block "blockable" mixed content.

content/browser/renderer_host/render_view_host_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_view_host_impl.h"
 
 #include <set>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 505 matching lines @@
 
   prefs.disable_reading_from_canvas = command_line.HasSwitch(
       switches::kDisableReadingFromCanvas);
 
   prefs.strict_mixed_content_checking = command_line.HasSwitch(
       switches::kEnableStrictMixedContentChecking);
 
   prefs.strict_powerful_feature_restrictions = command_line.HasSwitch(
       switches::kEnableStrictPowerfulFeatureRestrictions);
 
+  const std::string blockable_mixed_content_group =
+      base::FieldTrialList::FindFullName("BlockableMixedContent");
+  prefs.strictly_block_blockable_mixed_content =
+      blockable_mixed_content_group == "StrictlyBlockBlockableMixedContent";
+
   prefs.v8_cache_options = GetV8CacheOptions();
 
   GetContentClient()->browser()->OverrideWebkitPrefs(this, &prefs);
   return prefs;
 }
 
 void RenderViewHostImpl::SuppressDialogsUntilSwapOut() {
   Send(new ViewMsg_SuppressDialogsUntilSwapOut(GetRoutingID()));
 }
 
@@ skipping 881 matching lines @@
     if (!policy->CanReadFile(GetProcess()->GetID(), file))
       policy->GrantReadFile(GetProcess()->GetID(), file);
   }
 }
 
 void RenderViewHostImpl::SelectWordAroundCaret() {
   Send(new ViewMsg_SelectWordAroundCaret(GetRoutingID()));
 }
 
 }  // namespace content