Improve how DocumentMarkerController updates markers in response to text edits

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

Index: third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
diff --git a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
index e1c9096c5b4aad0636e4b894d474edcfd4db26b6..9d22eb74d1707a33e9abaeee72db08537d4fe9ba 100644
--- a/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
+++ b/third_party/WebKit/Source/core/editing/markers/DocumentMarker.h
@@ -26,6 +26,7 @@
 #include "core/CoreExport.h"
 #include "platform/graphics/Color.h"
 #include "platform/heap/Handle.h"
+#include "wtf/Optional.h"
 #include "wtf/VectorTraits.h"
 #include "wtf/text/WTFString.h"
 
@@ -164,6 +165,15 @@ class CORE_EXPORT DocumentMarker : public GarbageCollected<DocumentMarker> {
   void SetIsActiveMatch(bool);
   void ClearDetails() { details_.Clear(); }
 
+  struct MarkerOffsets {
+    unsigned start_offset;
+    unsigned end_offset;
+  };
+
+  Optional<MarkerOffsets> ComputeOffsetsAfterShift(unsigned offset,
+                                                   unsigned old_length,
+                                                   unsigned new_length) const;
+
   // Offset modifications are done by DocumentMarkerController.
   // Other classes should not call following setters.
   void SetStartOffset(unsigned offset) { start_offset_ = offset; }