Deprecate the allowfullscreen exemption for <video>

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index 049a0e092c1e191d785ee16567ad874156d5ba9f..22920273a448de589bd90fdfd0f097fac6c8481d 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -917,6 +917,9 @@ String UseCounter::deprecationMessage(Feature feature)
     case CSSSelectorPseudoShadow:
         return "::shadow pseudo-element is deprecated. See https://www.chromestatus.com/features/6750456638341120 for more details.";
 
+    case VideoFullscreenAllowedExemption:
+        return "Entering fullscreen in an <iframe> with no allowfullscreen attribute is deprecated and will stop working in M46, around October 2015. Please use the allowfullscreen attribute.";

[falken, 2015/06/08 03:22:29]

Hum, I don't know whether Blink should refer to Chrome milestones, since there
can be other embedders. But I see other strings here do it too.

[philipj_slow, 2015/06/09 19:17:17]

Yeah, this looks a bit odd, but Chromium is the only Blink embedder and there's
no other human-understandable version number we could really use here.

+
     // Features that aren't deprecated don't have a deprecation message.
     default:
         return String();