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

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

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index a2acaddeb2943db66145e50fe44d91f8bcd0e57c..35185b127cd6c62f72d40bac5d8755b9f2de92b4 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -758,7 +758,9 @@ class CORE_EXPORT Document : public ContainerNode,
 
   void didInsertText(Node*, unsigned offset, unsigned length);
   void didRemoveText(Node*, unsigned offset, unsigned length);
-  void didMergeTextNodes(Text& oldNode, unsigned offset);
+  void didMergeTextNodes(const Text& mergedNode,
+                         const Text& nodeToBeRemoved,
+                         unsigned oldLength);
   void didSplitTextNode(const Text& oldNode);
 
   void clearDOMWindow() { m_domWindow = nullptr; }