Add a counter for postMessage from insecure to secure top-level frames

third_party/WebKit/Source/core/frame/DOMWindow.cpp

Index: third_party/WebKit/Source/core/frame/DOMWindow.cpp
diff --git a/third_party/WebKit/Source/core/frame/DOMWindow.cpp b/third_party/WebKit/Source/core/frame/DOMWindow.cpp
index 3e4723950ddf5d5b5f8e47f46bf2669a907f6d40..29fa67e69cc62d751d66319ca600a49d24719e84 100644
--- a/third_party/WebKit/Source/core/frame/DOMWindow.cpp
+++ b/third_party/WebKit/Source/core/frame/DOMWindow.cpp
@@ -233,12 +233,17 @@ void DOMWindow::postMessage(PassRefPtr<SerializedScriptValue> message,
           : KURL(KURL(),
                  frame()->securityContext()->getSecurityOrigin()->toString());
   if (MixedContentChecker::isMixedContent(sourceDocument->getSecurityOrigin(),
-                                          targetUrl))
+                                          targetUrl)) {
     UseCounter::count(frame(), UseCounter::PostMessageFromSecureToInsecure);
-  else if (MixedContentChecker::isMixedContent(
-               frame()->securityContext()->getSecurityOrigin(),
-               sourceDocument->url()))
+  } else if (MixedContentChecker::isMixedContent(
+                 frame()->securityContext()->getSecurityOrigin(),
+                 sourceDocument->url())) {
     UseCounter::count(frame(), UseCounter::PostMessageFromInsecureToSecure);
+    if (frame()->isMainFrame()) {

[Mike West, 2017/01/23 08:59:22]

That is, I think the goal of the counter is to determine how often a user would
see the UI degrade from secure to insecure; to determine that, I think you want
to figure out if the top-level frame is secure or not. That is, given a message
to `grandchild` in the tree `top -> child -> grandchild`, this new counter would
never trigger, even if `grandchild`, `child`, and `top` were all secure.

WDYT about changing this to something like `if
(MixedContentChecker::isMixedContent(frame()->tree().top()->securityContext()->getSecurityOrigin(),
sourceDocument->url()))`?

+      UseCounter::count(frame(),
+                        UseCounter::PostMessageFromInsecureToSecureToplevel);
+    }
+  }
 
   MessageEvent* event =
       MessageEvent::create(std::move(channels), std::move(message),