Add a UseCounter for execCommand with INPUT or TEXTAREA element.

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 38f7ad29e6c594c1cc17abd4e7ca0a12f465d8bc..1616dd6796371cbf7736758e8b299bfc3d454aee 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -4393,6 +4393,8 @@ bool Document::execCommand(const String& commandName, bool, const String& value,
         exceptionState.throwDOMException(InvalidStateError, "execCommand is only supported on HTML documents.");
         return false;
     }
+    if (focusedElement() && isHTMLTextFormControlElement(*focusedElement()))
+        UseCounter::count(*this, UseCounter::ExecCommandOnInputOrTextarea);
 
     // We don't allow recursive |execCommand()| to protect against attack code.
     // Recursive call of |execCommand()| could be happened by moving iframe