Make SynchronousMutationObserver::didMergeTextNodes() to take both merged and merging nodes

third_party/WebKit/Source/core/dom/SynchronousMutationObserver.h

Index: third_party/WebKit/Source/core/dom/SynchronousMutationObserver.h
diff --git a/third_party/WebKit/Source/core/dom/SynchronousMutationObserver.h b/third_party/WebKit/Source/core/dom/SynchronousMutationObserver.h
index 2df1926954e0653d6b7682e6c219103e37621938..ad0311ca64c0168fee3532f37ab0ec9647d59f5a 100644
--- a/third_party/WebKit/Source/core/dom/SynchronousMutationObserver.h
+++ b/third_party/WebKit/Source/core/dom/SynchronousMutationObserver.h
@@ -14,6 +14,7 @@ namespace blink {
 class CharacterData;
 class ContainerNode;
 class Document;
+class NodeWithIndex;
 class Text;
 
 // This class is a base class for classes which observe DOM tree mutation
@@ -42,10 +43,11 @@ class CORE_EXPORT SynchronousMutationObserver
   // Called after child nodes changed.
   virtual void didChangeChildren(const ContainerNode&);
 
-  // TODO(yosin): We should use |const Text& oldNode|.
-  // Called after characters in |oldNode| is appended at |offset| in
-  // |oldNdoe->previousSibling()|.
-  virtual void didMergeTextNodes(Text& oldNode, unsigned offset);
+  // Called after characters in |nodeToBeRemoved| is appended into |mergedNode|.
+  // |oldLength| holds length of |mergedNode| before merge.
+  virtual void didMergeTextNodes(const Text& mergedNode,
+                                 const NodeWithIndex& nodeToBeRemovedWithIndex,
+                                 unsigned oldLength);
 
   // Called just after node tree |root| is moved to new document.
   virtual void didMoveTreeToNewDocument(const Node& root);