Revert "Mixed content iframe checks should use top"

Source/core/loader/DocumentLoader.cpp

Index: Source/core/loader/DocumentLoader.cpp
diff --git a/Source/core/loader/DocumentLoader.cpp b/Source/core/loader/DocumentLoader.cpp
index b296443799ad26f716e5029b0388f5838e5aa972..e8808e0dcee2844b2acdf384f851241b2e84f0b2 100644
--- a/Source/core/loader/DocumentLoader.cpp
+++ b/Source/core/loader/DocumentLoader.cpp
@@ -486,9 +486,9 @@ void DocumentLoader::willSendRequest(ResourceRequest& newRequest, const Resource
     if (newRequest.cachePolicy() == UseProtocolCachePolicy && isPostOrRedirectAfterPost(newRequest, redirectResponse))
         newRequest.setCachePolicy(ReloadIgnoringCacheData);
 
-    Frame* top = m_frame->tree()->top();
-    if (top) {
-        if (!top->loader()->mixedContentChecker()->canRunInsecureContent(top->document()->securityOrigin(), newRequest.url())) {
+    Frame* parent = m_frame->tree()->parent();
+    if (parent) {
+        if (!parent->loader()->mixedContentChecker()->canRunInsecureContent(parent->document()->securityOrigin(), newRequest.url())) {
             cancelMainResourceLoad(frameLoader()->cancelledError(newRequest));
             return;
         }