Introduce previousPositionOf() for VisiblePosition

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 e10c51a1e397a7ff1c879442ccfb94ce9d6db2a4..0be32836a8066f3fa3cf1fd2df20a140f410e2a7 100644
--- a/Source/core/editing/VisibleSelection.cpp
+++ b/Source/core/editing/VisibleSelection.cpp
@@ -429,7 +429,7 @@ void VisibleSelection::setStartRespectingGranularity(TextGranularity granularity
     case ParagraphGranularity: {
         VisiblePosition pos(m_start, m_affinity);
         if (isStartOfLine(pos) && isEndOfEditableOrNonEditableContent(pos))
-            pos = pos.previous();
+            pos = previousPositionOf(pos);
         m_start = startOfParagraph(pos).deepEquivalent();
         break;
     }