Add deprecation warnings to old powerful features on insecure origins.

Source/core/dom/Fullscreen.cpp

Index: Source/core/dom/Fullscreen.cpp
diff --git a/Source/core/dom/Fullscreen.cpp b/Source/core/dom/Fullscreen.cpp
index 552abaaa706744252e467126c67bdaaa4c3dd2ef..48056019a28429f8e6af8727a4d40e244980b93f 100644
--- a/Source/core/dom/Fullscreen.cpp
+++ b/Source/core/dom/Fullscreen.cpp
@@ -204,6 +204,15 @@ void Fullscreen::documentWasDisposed()
 
 void Fullscreen::requestFullscreen(Element& element, RequestType requestType)
 {
+    // It is required by isPrivilegedContext() but isn't
+    // actually used. This could be used later if a warning is shown in the

[philipj_slow, 2015/05/01 22:36:58]

The countDeprecation is the console warning, is there any chance that this
errorMessage will ever be used? Some other clients throw exceptions using this
message, but that will not make sense for the Fullscreen API. I think these
checks should be in fullscreenIsSupported, which is the place in the spec which
allows taking this into consideration. That would also ensure that
document.fullscreenEnabled is false if fullscreen will always fail, if it's made
to return false if (frame()->settings()->strictPowerfulFeatureRestrictions()).

[jww, 2015/05/05 21:29:53]

I think that's an accurate description of where it should be blocked in the long
term, but it appears to me to be the wrong place to measure usage. That is, I
don't think we don't want to measure that fullscreen is being used until
requestFullscreen is actually called.

[philipj_slow, 2015/05/06 07:43:55]

The fullscreen element ready check is only used in requestFullscreen() in both
spec and implementation. (I didn't check this when I commented, though, so your
skepticism is warranted.)

If you want to move this to the ready check I'll be happy to review, but there's
no hurry really.

+    // developer console.
+    String errorMessage;
+    if (document()->isPrivilegedContext(errorMessage))
+        UseCounter::count(document(), UseCounter::FullscreenSecureOrigin);
+    else
+        UseCounter::countDeprecation(document(), UseCounter::FullscreenInsecureOrigin);
+
     // Ignore this request if the document is not in a live frame.
     if (!document()->isActive())
         return;