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

Source/core/editing/VisibleSelection.cpp

Index: Source/core/editing/VisibleSelection.cpp
diff --git a/Source/core/editing/VisibleSelection.cpp b/Source/core/editing/VisibleSelection.cpp
index c0181c12bd7402842a092f053a0dc055849a9406..a331d3c3e5e03689fbe629cb295f0bdcf23c668b 100644
--- a/Source/core/editing/VisibleSelection.cpp
+++ b/Source/core/editing/VisibleSelection.cpp
@@ -216,12 +216,12 @@ PositionInComposedTree VisibleSelection::endInComposedTree() const
     return m_endInComposedTree;
 }
 
-PassRefPtrWillBeRawPtr<Range> VisibleSelection::firstRange() const
+PassRefPtrWillBeRawPtr<Range> firstRangeOf(const VisibleSelection& selection)
 {
-    if (isNone())
+    if (selection.isNone())
         return nullptr;
-    Position start = m_start.parentAnchoredEquivalent();
-    Position end = m_end.parentAnchoredEquivalent();
+    Position start = selection.start().parentAnchoredEquivalent();
+    Position end = selection.end().parentAnchoredEquivalent();
     return Range::create(*start.document(), start, end);
 }