Add a use counter and deprecation message for showModalDialog

Source/core/page/UseCounter.cpp

Index: Source/core/page/UseCounter.cpp
diff --git a/Source/core/page/UseCounter.cpp b/Source/core/page/UseCounter.cpp
index e821e0f14abe231f6998f6651ae8b507fa1b0475..c25a159191f83f888a8c99b063688a9ddbed1a9e 100644
--- a/Source/core/page/UseCounter.cpp
+++ b/Source/core/page/UseCounter.cpp
@@ -681,6 +681,9 @@ String UseCounter::deprecationMessage(Feature feature)
     case ScrollLeftBodyNotQuirksMode:
         return "body.scrollLeft is deprecated in strict mode. Please use 'documentElement.scrollLeft' if in strict mode and 'body.scrollLeft' only if in quirks mode.";
 
+    case ShowModalDialog:
+        return "Blink is considering deprecating showModalDialog. Please consider using window.open and postMessage instead.";

[adamk, 2013/10/30 22:31:25]

The use of "Blink" here is a little odd; maybe "Chromium" would be clearer? I
guess I'm wondering why you're equivocating (I think you should at least drop
the second use of "consider" in this message, instead saying "Please use ...";
even if we didn't remove showModalDialog, everyone would be better off not using
it). 

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