Add metrics for setting document.domain.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 7b8f91baf1a3090645b4bd4bf4867742557e27a2..c5adc02aed043c97f297ad888307b18ee32919bd 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -3925,6 +3925,8 @@ String Document::domain() const
 
 void Document::setDomain(const String& newDomain, ExceptionState& exceptionState)
 {
+    UseCounter::count(*this, UseCounter::DocumentSetDomain);
+
     if (isSandboxed(SandboxDocumentDomain)) {
         exceptionState.throwSecurityError("Assignment is forbidden for sandboxed iframes.");
         return;