Don't merge adjacent composition markers.

Source/core/editing/markers/DocumentMarkerController.cpp

Index: Source/core/editing/markers/DocumentMarkerController.cpp
diff --git a/Source/core/editing/markers/DocumentMarkerController.cpp b/Source/core/editing/markers/DocumentMarkerController.cpp
index b0040ff6f32e4fc55837210d00959c7c55ff9358..e1bca8ab4864bd506749a82797192833abe715ec 100644
--- a/Source/core/editing/markers/DocumentMarkerController.cpp
+++ b/Source/core/editing/markers/DocumentMarkerController.cpp
@@ -214,7 +214,7 @@ void DocumentMarkerController::addMarker(Node* node, const DocumentMarker& newMa
     if (list->isEmpty() || list->last()->endOffset() < newMarker.startOffset()) {
         list->append(newRenderedMarker.release());
     } else {
-        if (newMarker.type() != DocumentMarker::TextMatch) {
+        if (newMarker.type() != DocumentMarker::TextMatch && newMarker.type() != DocumentMarker::Composition) {
             mergeOverlapping(list.get(), newRenderedMarker.release());
         } else {
             MarkerList::iterator pos = std::lower_bound(list->begin(), list->end(), &newMarker, startsFurther);