Revert of [Editing][Codehealth] Replace Position::uptream/downstream to...

Revert of [Editing][Codehealth] Replace Position::uptream/downstream to mostBackward/ForwardCaretPosition. (patchset #1 id:1 of https://codereview.chromium.org/1306743002/ )

Reason for revert:
This patch misused each other.
See:
 https://codereview.chromium.org/1310433004/

Original issue's description:
> [Editing][Codehealth] Replace Position::uptream/downstream to 
> mostBackward/ForwardCaretPosition
> 
> Position::upstream calls just VisibleUnit.cpp::mostForwardCaretPosition and also 
> downstream:
> https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/c
> ore/editing/Position.cpp&l=484&cl=GROK
> 
> This CL replaces it.
> We will replace all upstream/downstream and remove them.
> 
> BUG=518738
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200977

TBR=yosin@chromium.org,tkent@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=518738

Review URL: https://codereview.chromium.org/1304133002

git-svn-id: svn://svn.chromium.org/blink/trunk@200978 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/layout/HitTestResult.cpp

@@ -163,7 +163,7 @@ PositionWithAffinity HitTestResult::position() const
     if (!layoutObject)
         return PositionWithAffinity();
     if (m_innerPossiblyPseudoNode->isPseudoElement() && m_innerPossiblyPseudoNode->pseudoId() == BEFORE)
-        return mostBackwardCaretPosition(Position(m_innerNode, PositionAnchorType::BeforeChildren));
+        return Position(m_innerNode, PositionAnchorType::BeforeChildren).downstream();
     return layoutObject->positionForPoint(localPoint());
 }
 

third_party/WebKit/Source/core/layout/LayoutObject.cpp

@@ -2992,10 +2992,10 @@ PositionWithAffinity LayoutObject::createPositionWithAffinity(int offset, TextAf
         if (!node->hasEditableStyle()) {
             // If it can be found, we prefer a visually equivalent position that is editable.
             const Position position = Position(node, offset);
-            Position candidate = mostBackwardCaretPosition(position, CanCrossEditingBoundary);
+            Position candidate = position.downstream(CanCrossEditingBoundary);
             if (candidate.anchorNode()->hasEditableStyle())
                 return PositionWithAffinity(candidate, affinity);
-            candidate = mostForwardCaretPosition(position, CanCrossEditingBoundary);
+            candidate = position.upstream(CanCrossEditingBoundary);
             if (candidate.anchorNode()->hasEditableStyle())
                 return PositionWithAffinity(candidate, affinity);
         }

third_party/WebKit/Source/core/layout/LayoutView.cpp

@@ -803,11 +803,11 @@ void LayoutView::commitPendingSelectionAlgorithm()
     // as the start of the selection, the selection painting code will think that content on the line containing 'foo' is selected
     // and will fill the gap before 'bar'.
     PositionType startPos = Strategy::selectionStart(selection);
-    PositionType candidate = mostBackwardCaretPosition(startPos);
+    PositionType candidate = startPos.downstream();
     if (isVisuallyEquivalentCandidate(candidate))
         startPos = candidate;
     PositionType endPos = Strategy::selectionEnd(selection);
-    candidate = mostForwardCaretPosition(endPos);
+    candidate = endPos.upstream();
     if (isVisuallyEquivalentCandidate(candidate))
         endPos = candidate;