Add CompositionMarkerList in preparation for DocumentMarkerController refactor

third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp

Index: third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
diff --git a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
index b18b3fd88304206850783d3ee5de7a20483edd5f..7465262ac7324e34a6102a1154e37cefc431b5c4 100644
--- a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
+++ b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.cpp
@@ -166,6 +166,53 @@ DocumentMarker::DocumentMarker(const DocumentMarker& marker)
       m_endOffset(marker.endOffset()),
       m_details(marker.details()) {}
 
+DocumentMarker::ShiftMarkerResult DocumentMarker::getShiftedMarkerPosition(
+    unsigned offset,
+    unsigned oldLength,
+    unsigned newLength) const {
+  ShiftMarkerResult result;
+  result.newStartOffset = startOffset();
+  result.newEndOffset = endOffset();
+  result.shouldRemoveMarker = false;
+
+  // algorithm inspired by https://dom.spec.whatwg.org/#concept-cd-replace
+  // but with some changes
+
+  // Deviation from the concept-cd-replace algorithm: second condition in the
+  // next line (don't include text inserted immediately before a marker in the
+  // marked range, but do include the new text if it's replacing text in the
+  // marked range)
+  if (startOffset() > offset || (startOffset() == offset && oldLength == 0)) {
+    if (startOffset() <= offset + oldLength) {
+      // Marker start was in the replaced text. Move to end of new text
+      // (Deviation from the concept-cd-replace algorithm: that algorithm
+      // would move to the beginning of the new text here)
+      result.newStartOffset = offset + newLength;
+    } else {
+      // Marker start was after the replaced text. Shift by length
+      // difference
+      result.newStartOffset = startOffset() + newLength - oldLength;
+    }
+  }
+
+  if (endOffset() > offset) {
+    // Deviation from the concept-cd-replace algorithm: < instead of <= in
+    // the next line
+    if (endOffset() < offset + oldLength) {
+      // Marker end was in the replaced text. Move to beginning of new text
+      result.newEndOffset = offset;
+    } else {
+      // Marker end was after the replaced text. Shift by length difference
+      result.newEndOffset = endOffset() + newLength - oldLength;
+    }
+  }
+
+  if (result.newStartOffset >= result.newEndOffset)
+    result.shouldRemoveMarker = true;
+
+  return result;
+}
+
 void DocumentMarker::shiftOffsets(int delta) {
   m_startOffset += delta;
   m_endOffset += delta;