Introduce firstRangeOf() as replacement of VisibleSelection::firstRange()

Source/core/editing/commands/EditorCommand.cpp

Index: Source/core/editing/commands/EditorCommand.cpp
diff --git a/Source/core/editing/commands/EditorCommand.cpp b/Source/core/editing/commands/EditorCommand.cpp
index 546c0dabfb9d5008efae0e4428648de28f9ba2ae..b60230ee77a528557312c21863d11d98b9f84cec 100644
--- a/Source/core/editing/commands/EditorCommand.cpp
+++ b/Source/core/editing/commands/EditorCommand.cpp
@@ -1436,7 +1436,7 @@ static String valueFormatBlock(LocalFrame& frame, Event*)
     const VisibleSelection& selection = frame.selection().selection();
     if (!selection.isNonOrphanedCaretOrRange() || !selection.isContentEditable())
         return "";
-    Element* formatBlockElement = FormatBlockCommand::elementForFormatBlockCommand(selection.firstRange().get());
+    Element* formatBlockElement = FormatBlockCommand::elementForFormatBlockCommand(firstRangeOf(selection).get());
     if (!formatBlockElement)
         return "";
     return formatBlockElement->localName();