Introduce composed tree version of startOfWord()

Source/core/editing/VisibleUnits.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 810 matching lines @@
         needMoreContext = true;
         return 0;
     }
     needMoreContext = false;
     int start, end;
     U16_BACK_1(characters, 0, offset);
     findWordBoundary(characters, length, offset, &start, &end);
     return start;
 }
 
-VisiblePosition startOfWord(const VisiblePosition& c, EWordSide side)
+template <typename Strategy>
+static VisiblePositionTemplate<Strategy> startOfWordAlgorithm(const VisiblePositionTemplate<Strategy>& c, EWordSide side)
 {
-    // FIXME: This returns a null VP for c at the start of the document
-    // and side == LeftWordIfOnBoundary
-    VisiblePosition p = c;
+    // TODO(yosin) This returns a null VP for c at the start of the document
+    // and |side| == |LeftWordIfOnBoundary|
+    VisiblePositionTemplate<Strategy> p = c;
     if (side == RightWordIfOnBoundary) {
         // at paragraph end, the startofWord is the current position
         if (isEndOfParagraph(c))
             return c;
 
         p = nextPositionOf(c);
         if (p.isNull())
             return c;
     }
     return previousBoundary(p, startWordBoundary);
 }
 
+VisiblePosition startOfWord(const VisiblePosition& c, EWordSide side)
+{
+    return startOfWordAlgorithm<EditingStrategy>(c, side);
+}
+
+VisiblePositionInComposedTree startOfWord(const VisiblePositionInComposedTree& c, EWordSide side)
+{
+    return startOfWordAlgorithm<EditingInComposedTreeStrategy>(c, side);
+}
+
 static unsigned endWordBoundary(const UChar* characters, unsigned length, unsigned offset, BoundarySearchContextAvailability mayHaveMoreContext, bool& needMoreContext)
 {
     ASSERT(offset <= length);
     if (mayHaveMoreContext && endOfFirstWordBoundaryContext(characters + offset, length - offset) == static_cast<int>(length - offset)) {
         needMoreContext = true;
         return length;
     }
     needMoreContext = false;
     return findWordEndBoundary(characters, length, offset);
 }
@@ skipping 2343 matching lines @@
 {
     return previousPositionOfAlgorithm<EditingStrategy>(visiblePosition, rule);
 }
 
 VisiblePositionInComposedTree previousPositionOf(const VisiblePositionInComposedTree& visiblePosition, EditingBoundaryCrossingRule rule)
 {
     return previousPositionOfAlgorithm<EditingInComposedTreeStrategy>(visiblePosition, rule);
 }
 
 } // namespace blink